Methods of making an elastomer composite reinforced with silica and products containing same

ABSTRACT

Methods to make a silica elastomer composite with a destabilized dispersion of a never-dried, or as-produced, precipitated silica are described, along with silica elastomer composites made from the methods. The advantages achieved with the methods are further described.

The present invention relates to methods of making silica elastomercomposites. More particularly, the present invention relates to a silicareinforced elastomer composite formed by a wet masterbatch method.

Numerous products of commercial significance are formed of elastomericcompositions wherein particulate reinforcing material is dispersed inany of various synthetic elastomers, natural rubber or elastomer blends.Carbon black and silica, for example, are widely used as reinforcingagents in natural rubber and other elastomers. It is common to produce amasterbatch, that is, a premixture of reinforcing material, elastomer,and various optional additives, such as extender oil. Numerous productsof commercial significance are formed of such elastomeric compositions.Such products include, for example, vehicle tires wherein differentelastomeric compositions may be used for the tread portion, sidewalls,wire skim and carcass. Other products include, for example, engine mountbushings, conveyor belts, windshield wipers, seals, liners, wheels,bumpers, and the like.

Good dispersion of particulate reinforcing agents in rubber compoundshas been recognized for some time as one of the most importantobjectives for achieving good quality and consistent productperformance, and considerable effort has been devoted to the developmentof methods to improve dispersion quality. Masterbatch and other mixingoperations have a direct impact on mixing efficiency and on dispersionquality. In general, for instance, when carbon black is employed toreinforce rubber, acceptable carbon black macro-dispersions can often beachieved in a dry-mixed masterbatch. However, high quality, uniformdispersion of silica by dry-mix processes poses difficulties, andvarious solutions have been offered by the industry to address thisproblem, such as precipitated silica in the form of “highly dispersiblesilica” or “HDS” flowable granules. More intensive mixing can improvesilica dispersion, but also can degrade the elastomer into which thefiller is being dispersed. This is especially problematic in the case ofnatural rubber, which is highly susceptible to mechanical/thermaldegradation.

In addition to dry mixing techniques, it is known to feed elastomerlatex or polymer solution and a carbon black or silica slurry to anagitated tank. Such “wet masterbatch” techniques can be used withnatural rubber latex and emulsified synthetic elastomers, such asstyrene butadiene rubber (SBR). However, while this wet technique hasshown promise when the filler is carbon black, this wet technique, whenthe filler is silica, poses challenges to achieving acceptable elastomercomposite. Specific techniques for producing wet masterbatch, such asthe one disclosed in U.S. Pat. No. 6,048,923, the contents of which areincorporated by reference herein, have not been effective for producingelastomer composites employing silica particles as the sole or principalreinforcing agent.

Accordingly, there is a need to improve methods that incorporate silicain elastomer composites in a wet masterbatch process, such as one thatmakes use of combining two fluids together under continuous, high energyimpact conditions, so as to achieve an acceptable elastomer compositecomprising silica particles as the sole or principal reinforcing agent,as described in U.S. Patent Application No. 62/192,891 and 62/294,599.Now, further improvements have been developed to integrate themanufacture of particulate silica into the production of elastomercomposites in wet masterbatch processes, wherein silica drying steps areeliminated.

Precipitated silica is generally produced by acidifying a solution ofsilicate, which leads to polymerization, nucleation and growth of silicaparticles in an aqueous medium. The growing particles can collide,leading to aggregation, which can be consolidated by further depositionof silica on particle surfaces. The final size, surface area andstructure of the particles are controlled by controlling silicateconcentration, temperature, pH and metal ion content. At the end of theparticle-forming process, an aqueous slurry of particles is obtained.This slurry undergoes a solid-liquid separation, usually comprisingfiltration such as by means of a filter press, belt filter or vacuumfilter. The filtered particles are then washed to remove salt and othersoluble substances and further filtered to give a filter cake. Thefilter cake typically contains 60-90% water by weight and 10-40% silicaon a total filter cake weight basis. A typical production process isdescribed in U.S. Pat. No. 7,250,463, incorporated in its entirety byreference herein.

Conventionally the wet filter cake is dried relatively slowly in ovens,or rotating dryers. Silica produced that way is generally considereddifficult to disperse in rubber. An alternative drying process involvesrapid heating to high temperatures for a short period of time, forexample in a spray dryer. Precipitated silica produced this waygenerally gives much better dispersability in rubber. It is thought thatduring conventional drying, a combination of high capillary forcesexerted by thin layers of water and chemical reactions between silanolgroups on adjacent particles, leads to compact agglomerates with strongbonds between particles. The most significant chemical reaction iscondensation, leading to siloxane bonds. This reaction is accelerated byheat and by removal of water. The strong bonds that are formed betweenparticles cannot be easily broken during rubber mixing and hence,dispersion tends to be poor. During the rapid drying process, theresidence time of the particles at high temperature is much shorter,providing less time for particle rearrangement or compaction and fewercondensation reactions. This leads to a lower number of bonds or strongcontacts between silica particles, and therefore better rubberdispersion. However, it is not thought that silica particle-particlebonding is completely eliminated in the rapid-drying process, justreduced relative to the conventional process.

Thus, it would be very beneficial if a method could be developed thatavoided or reduced the amount of drying of silica before itsincorporation into rubber (elastomers). The advantages not only wouldprovide a better quality elastomer composite reinforced with silica butalso provide savings in the overall processes that utilize silica sincethe time and cost of drying the silica before its use can be avoided orreduced.

SUMMARY OF THE PRESENT INVENTION

A feature of the present invention is to provide methods to produceelastomer composites using a wet masterbatch process which permits theuse of as-produced silica in wet form or silica not subjected to dryingbefore dispersing in the elastomer, and yet achieves desirable silicaelastomer composites.

To achieve these and other advantages, and in accordance with thepurposes of the present invention, as embodied and broadly describedherein, the present invention relates to a method of making elastomercomposite in a wet masterbatch process that includes, but is not limitedto, the use of a fluid that includes an elastomer latex, and the use ofan additional fluid that includes a destabilized dispersion ofparticulate silica, where the silica has been obtained without dryingthe silica to a water content of less than 60% by weight. The two fluidsare combined together under continuous flow conditions and selectedvelocities. The combining is such that the silica is dispersed withinthe elastomer latex and, in parallel (or almost parallel), the elastomerlatex is transformed from a liquid to a solid or semi-solid elastomercomposite, such as to a solid or semi-solid silica-containing continuousrubber phase. This can occur, for instance, in about two seconds or lesssuch as a fraction of a second, due to the one fluid impacting the otherfluid with sufficient energy to cause the uniform and intimatedistribution of silica particles in the elastomer. The use of adestabilized dispersion of silica that is not dried beforehand, in thismasterbatch process enables formation of an elastomer composite withdesirable properties.

The present invention further relates to elastomer composites formedfrom any one or more of the processes of the present invention. Thepresent invention also relates to articles that are made from or includethe elastomer composite(s) of the present invention.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are intended to provide a further explanation of the presentinvention as claimed.

The accompanying drawings, which are incorporated in and constitute apart of this application, illustrate various features of the presentinvention and, together with the description, serve to explain theprinciples of the present invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A illustrates an exemplary mixing apparatus in accordance withProcess A;

FIG. 1B illustrates an exemplary mixing apparatus in accordance withProcess B;

FIG. 1C illustrates an exemplary mixing apparatus having an additionalinlet, in accordance with Process B; and

FIG. 2 is a block diagram of various steps that can occur in theformation of the elastomer composite of the present invention and inmaking rubber compounds with such elastomer composites.

FIG. 3 is a block diagram of various optional steps that can occur tosupply silica used in the formation of the silica elastomer composite ofthe present invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The present invention relates to the selective and strategicintroduction of silica, as-produced, in wet or never-dried form, into anelastomer latex in an integrated, continuous, or semi-continuous rapid,wet masterbatch process. Selected steps in the semi-continuous processmay be carried out as batch processes. This process can be carried outin a semi-confined reaction zone, such as a tubular mixing chamber orother mixing chamber of an apparatus suitable for carrying out such aprocess under controlled volumetric flow and velocity parameters,leading to beneficial properties that would not be achieved, but forthis selective and strategic use of silica. As explained in furtherdetail herein, by ‘selective’, the present invention uses a destabilizeddispersion of silica. And, by ‘strategic’ introduction, the presentinvention uses at least two separate fluids, one fluid that includes anelastomer latex, and another fluid that includes the destabilizeddispersion of particulate silica. The two fluids can be pumped ortransferred into a reaction zone, such as a semi-confined reaction zone.The two fluids can be combined under continuous flow conditions, andunder selected volumetric flow and velocity conditions. The combiningunder pressure with selected differential velocity conditions issufficiently energetic that the silica can be distributed in two secondsor less, such as in milliseconds, within the elastomer latex, and theelastomer latex is transformed from a liquid to a solid phase, such asto a silica elastomer composite in the form of a solid or semi-solidsilica-containing continuous rubber phase.

The present invention relates in part, to a method of producing a silicaelastomer composite, comprising, consisting essentially of, consistingof, or including:

(a) providing a continuous flow under pressure of at least a first fluidcomprising a destabilized dispersion of silica and providing acontinuous flow of a second fluid comprising elastomer latex, whereinthe silica has a wt % of silica of from about 6 wt % to about 35 wt %,based on the weight of the first fluid, and wherein the silica has neverbeen dried beforehand to a solids content of greater than 40% by weight;

(b) adjusting volumetric flows of the first fluid and the second fluidto yield an elastomer composite having a silica content of from about 15phr to about 180 phr; and

(c) combining the first fluid flow and the second fluid flow (forinstance in a semi-confined reaction zone) with sufficient impact todistribute the silica within the elastomer latex, to obtain a flow of asolid silica-containing continuous rubber phase or semi-solidsilica-containing continuous rubber phase. The method transforms theelastomer latex from a liquid to a flow of a solid or semi-solidsilica-containing continuous rubber phase. The silica-containingcontinuous rubber phase can be recovered as a substantially continuousflow of the solid or semi-solid silica-containing continuous rubberphase.

Further details and/or options for the methods of the present inventionare described below.

As used herein, “silica” means particulate silicon dioxide, or aparticle coated with silicon dioxide, and includes precipitated silicain any form, such as highly dispersible (HDS) granules, non-HDSgranules, silica aggregates and silica particles; colloidal silica;fumed silica; and any combinations thereof. Such silicon dioxide orsilicon dioxide coated particles may have been chemically treated toinclude functional groups bonded (attached (e.g., chemically attached)or adhered (e.g., adsorbed)) to the silica surface. Thus, “silica”includes any particle having a surface substantially consisting ofsilica or silica having functional groups bonded or attached to it.

As used herein, “wet silica” or “never-dried silica” means that thesilica material delivered to the wet masterbatch process of the presentinvention has not been subjected to any drying step or water removingstep that increases the solids content of the silica material to greaterthan 40% by weight, based on the total weight of the silica material(e.g., a silica dispersion or the silica reaction medium or the silicafilter cake). Put another way, the silica that is used in the methods ofthe present invention has a water or other aqueous fluid content of atleast 60 wt % (based on the total weight of the silica material) andtherefore can be considered a wet silica or never-dried silica.

For purposes of the invention and as used herein, “filter cake” is areference to a silica cake obtained by filtering the product of a silicaprecipitation reaction, and is considered a semi-solid product or pulp.The filter cake can be considered a non-slurry product. The filter cakevisually appears as a solid and not as a slurry. The filter cake canvisually be or have a pomice consistency. The filter cake can andgenerally does have a moisture content wherein the water content willgenerally be below 90 wt % based on the weight of the filter cake. Whilethe term “filter cake” is used, the formation of this type of productdoes not necessarily have to be achieved by filtering but can beachieved by other moisture removing processes or techniques, thoughfiltering is generally the preferred process to obtain the consistencyof a filter cake. The filter cake can have a water content of from about60 wt % to about 90 wt % which is from about 65 wt % to about 85 wt % orfrom about 70 wt % to about 90 wt % based on the weight of the filtercake.

For purposes of the invention and as used herein, “dispersion” means astable suspension of solid particles in aqueous fluid, wherein thecharge at the surface of the particles prevents particle agglomerationand the dispersion is characterized by a zeta potential magnitude ofgreater than or equal to 30 mV.

Zeta potential is used to measure stability of charged particles, suchas silica particles, dispersed in a fluid. Measurement of zeta potentialcan have a variance of, for instance+/−2 mV, and, as used herein, zetapotential magnitude refers to the absolute value of the number, e.g., azeta potential value of minus 30 mV has a greater magnitude than a zetapotential value of minus 10 mV.

As used herein, “destabilized dispersion” means a suspension of solidparticles in an aqueous fluid wherein the charge at the surface of theparticles has been reduced by the presence of an agent, or by treatmentof the solid particles, and is characterized by a zeta potentialmagnitude of less than 30 mV, or more preferably a zeta potential ofless than 28 mV or less than 25 mV. The aqueous fluid can be water, awater miscible fluid (e.g., alcohol or ether), partially water misciblefluid, or a mixture of fluids that contains at least a water miscible orpartially water miscible fluid.

As used herein, the terms “silica slurry” and “dispersion” mean adispersion of silica in an aqueous fluid, wherein the charge at thesurface of the silica prevents particle agglomeration and the dispersionis characterized by a zeta potential value with a magnitude of at least30 mV. A silica slurry or dispersion may be destabilized by treatmentwith sufficient agent(s), or by treatment of the silica, to reduce thecharge on the surface of the silica and the resulting destabilizedsilica slurry (or destabilized silica dispersion) is characterized by azeta potential magnitude of less than 30 mV.

As used herein, the terms “uniform” and “uniformly” are intended tomean, conventionally for those skilled in the art, that theconcentration of a component, for example, particulate filler, in anygiven fraction or percentage (e.g., 5%) of a volume is the same (e.g.,within 2%) as the concentration of that component in the total volume ofthe material in question, e.g., elastomer composite or dispersion. Thoseskilled in the art will be able to verify the statistical uniformity ofthe material, if required, by means of measurements of concentration ofthe component using several samples taken from various locations (forexample near the surface or deeper in the bulk).

As used herein, a “silica elastomer composite” means a masterbatch (apremixture of reinforcing material, elastomer, and various optionaladditives, such as extender oil) of coherent rubber comprising areinforcing amount (e.g., about 15 phr to about 180 phr) of dispersedsilica. Silica elastomer composite can contain optional, furthercomponents such as acid, salt, antioxidant, antidegradants, couplingagents, minor amounts (e.g., 10 wt % or less of total particulates) ofother particulates, processing aids, and/or extender oil, or anycombinations thereof.

As used herein, a “solid silica-containing continuous rubber phase”means a composite having a continuous rubber phase and a uniformlydispersed phase of silica and, for instance, up to 90%, by weight,aqueous fluid. The solid silica-containing continuous rubber phase maybe in the form of a continuous rope or worm. When compressed thesearticles release water. The solid silica-containing continuous rubberphase can contain optional, further components such as acid, salt,antioxidant, coupling agents, minor amounts of other particulates (e.g.,10 wt % or less of total particulates), and/or processing oil, or anycombinations thereof.

As used herein, a “semi-solid silica-containing continuous rubber phase”means a composite with a paste-like consistency, having asilica-containing, continuous rubber phase. The semi-solid product has acontinuous phase of rubber, with entrapped silica uniformly distributedthroughout the rubber phase. The semi-solid silica-containing continuousrubber phase remains coherent and expels water, while retaining solidscontent, upon further handling in one or more subsequent operationsselected to develop the paste-like or gel-like material into a solidsilica-containing continuous rubber phase.

As used herein, a “coherent” material is material existing in asubstantially unitary form that has been created by the adhesion of manysmaller parts, such as an elastic, solid mass of rubber created by theadhesion of many small rubber particles to each other.

As used herein, a “continuous flow” is a steady or constant flow of afluid without interruption from a supply source (e.g., tank). But, it isto be understood that temporary interruptions (e.g., a second or a fewminutes) of flow would still be considered a continuous flow (e.g., forinstance, when switching supply from various supply holding areas, suchas tanks and the like, or interrupting flows to accommodate downstreamunit processes or maintenance of the equipment).

The elastomer composite can be produced in a continuous flow processinvolving a liquid mixture of elastomer latex and destabilizeddispersion of silica. Any device, or apparatus or system can be used,provided the device, apparatus, or system can be operated such that aliquid mixture of elastomer latex and a destabilized silica dispersioncan be combined under continuous flow conditions and under controlledvolumetric flow, pressure, and velocity conditions, including, but notlimited to, the apparatus shown in FIG. 1A, 1B, or 1C, or any type ofeductor or ejector, or any other device arranged to combine a continuousflow of at least two flows of liquid under controlled volumetric flow,pressure, and velocity conditions into and through a reaction zone. Theapparatus described in US20110021664, U.S. Pat. No. 6,048,923,WO2011034589, WO2011034587, US20140316058, and WO2014110499 (eachincorporated in their entirety by reference) can be used or adapted tothe processes herein as well. Also, ejectors and eductors or syphonssuch as water jet eductors or steam jet syphons can be used (e.g, onescommercially available from Schutte & Koerting, Trevose, Pa.).

The apparatus can include various supply tanks, pipes, valves, metersand pumps to control volumetric flow, pressure, and velocity. Further,as indicated at inlet (3) in FIGS. 1A, 1B, and 1C, various types andsizes of nozzles or other orifice size control elements (3 a) can beemployed to control the velocity of the silica slurry. The volumetricdimension of the reaction zone (13) can be selected to provide desiredvolumetric flows of the fluids and the elastomer composite. The inlet(11) supplying the elastomer latex to the reaction zone may be taperedto provide different volumetric flow rates and velocities. Devices mayinclude an inlet (11) of uniform diameter, without any taper at theorifice leading to the reaction zone.

As indicated, one of the improvements with the present invention is theability to utilize silica in the first fluid wherein the silica hasnever been dried to a solids content of greater than 40% by weight,based on the weight of the silica material delivered to the wetmasterbatch process. In other words, the silica is obtained in theabsence of a drying step which will reduce the water content or moisturecontent to below 60 wt % based on the total weight of the silicamaterial. With the present invention, the ability to utilize silicawithout subjecting the silica to a drying step that reduces the watercontent to below 60 wt %, based on the total weight of the silicamaterial is significant. This permits, for instance, the method of thepresent invention to utilize silica, for instance precipitated silicawhile it is still a wet silica.

For instance, prior to providing a continuous flow under pressure of atleast a first fluid comprising a destabilized dispersion of silica inparticulate form, the method of the present invention can involvemethods to form a precipitated silica or other forms of silica. Thesteps can include acidifying a solution of silicate to obtain an aqueousslurry of precipitated silica. The step can further include filteringthe aqueous slurry of precipitated silica to obtain precipitated silicain the form of a filter cake that has a water content of from about 60wt % to about 90 wt % based on the weight of the filter cake. This watercontent can be from about 65 wt % to 90 wt %, 70 wt % to 90 wt %, or 60wt % to 80 wt %, and the like.

As another option, prior to wet masterbatch step (a) which involvesproviding a continuous flow under pressure of at least the first fluidcomprising the silica, the method can include acidifying a solution ofsilicate to obtain an aqueous slurry of precipitated silica having aninitial ionic concentration and then optionally adjusting this initialionic concentration to yield a solids content of from about 6 wt % toabout 35 wt % by weight based on the weight of the aqueous slurry. Thissolids content can be from about 10 wt % to about 25 wt % or from about15 wt % to about 20 wt %. The ionic concentration can be adjusted by theaddition of an acid and/or salt to the aqueous slurry as described indetail below. The aqueous slurry of precipitated silica can be fed, withor without adjustment of the ionic concentration, and optionally in theabsence of any filtering, to the reaction zone as the first fluid.

As another option, the method of the present invention can include,prior to wet masterbatch step (a) of providing a continuous flow underpressure of at least a first fluid containing the silica, the step ofacidifying a solution of silicate to obtain an aqueous slurry ofprecipitated silica and then, without drying the precipitated silica,adjusting the aqueous slurry of the precipitated silica to a solidscontent of from about 6 wt % to about 35% by weight based on the weightof the aqueous slurry. This solids content as before, can be from about10 wt % to about 25 wt % or from about 15 wt % to about 20 wt %.

As another option, prior to wet masterbatch step (a), the method caninclude acidifying a solution of silicate to obtain an aqueous slurry ofthe precipitated silica and then recovering the precipitated silica inthe absence of forming a filter cake wherein the precipitated silica hasa water content below 85 wt % based on the weight of the precipitatedsilica. As has been stated, the silica, for instance precipitatedsilica, can be used, as-produced, without any filter cake dryingbeforehand (namely prior to wet masterbatch step (a)) and/or not formedin any filter cake beforehand. This water content can be from about 84.9wt % to 60 wt % or from about 80 wt % to 60 wt % or from about 70 wt %to 60 wt % based on the weight of the precipitated silica.

As a further option, the method of the present invention can include theadditional steps, prior to wet masterbatch step (a), of acidifying asolution of silicate to obtain an aqueous slurry of precipitated silicaand then filtering the aqueous slurry of precipitated silica to obtainprecipitated silica in the form of a filter cake and then diluting thefilter cake with an aqueous solution and forming the aqueous slurry thatbecomes the first fluid. In this option, the filtering of the aqueousslurry of precipitated silica to obtain precipitated silica in the formof a filter cake can result in a water content that is lower thandesired, and therefore diluting the filter cake to increase the watercontent of the aqueous slurry is desirable for purposes of using thisaqueous slurry as the first fluid in the method of producing a silicaelastomer composite of the present invention. The filtering of theaqueous slurry to form the filter cake, and, optionally, the washing ofthe filter cake with an aqueous fluid, can result in a filter cakehaving a water content of from, for instance, 80 wt % to 40 wt % such asfrom about 80 wt % to 60 wt %, based on the weight of the filter cake.And, the diluting of this filter cake with an aqueous solution can leadto a water content of the aqueous slurry of from 94 wt % to about 65 wt% based on the weight of the first fluid.

A further option of the present invention involves, prior to wetmasterbatch step (a), of using silica coated carbon black particleswherein the present process involves the use of an aqueous slurry ofsilica coated carbon black particles that can be utilized without dryingof the reaction mixture that contains the silica coated carbon blackparticles. With this option of the present invention, silica coatedcarbon black particles can be made that are essentially wet silicacoated black particles and instead of going through the complex andcostly step of drying this material, it can be utilized in its wet statein the processes of the present invention. Thus, as an option, themethod of the present invention can include, prior to wet masterbatchstep (a), of adding an aqueous silicate solution to an aqueous slurry ofcarbon black particles to form a reaction mixture and adjusting thereaction mixture pH to deposit silica onto the carbon black particlesand forming an aqueous slurry of silica coated carbon black particles.Without drying the reaction mixture that contains the silica coatedcarbon black particles, the adjusting of this aqueous slurry containingthe silica coated carbon black particles to a solids content of fromabout 6 wt % to about 35 wt % based on the weight of the aqueous slurrycan be utilized as the first fluid in the present invention.

Examples of the type of carbon black and the reaction steps to form thesilica coated carbon black can be found in U.S. Pat. Nos. 6,541,113 and5,679,728, incorporated in their entirety by reference here.

For purposes of the present invention, the various options with regardto forming precipitated silica prior to wet masterbatch step (a) andutilizing the precipitated silica essentially in a form of a wet state,can involve acidifying a solution of silicate (e.g., sodium or potassiumsilicate) to obtain the aqueous slurry of precipitated silica that mayinclude an electrolyte such as a salt. Precipitated silica is usuallyproduced commercially by combining an aqueous solution of a solublemetal silicate, e.g., alkali metal silicate such as sodium silicate, andan acid so that colloidal particles will grow in weakly alkalinesolution and be coagulated by the alkali metal ions of the resultingsoluble alkali metal salt. Various acids may be used, including themineral acids and/or carbon dioxide. In the absence of a coagulant,silica is not precipitated from solution at any pH. The coagulant usedto effect precipitation may be the soluble alkali metal salt producedduring formation of the colloidal silica particles, it may be addedelectrolyte such as a soluble inorganic or organic salt, or it may be acombination of both. The deposition of silica on aggregates ofpreviously precipitated silica, has been referred to as reinforcement ofprecipitated silica. It has been found that by controlling theconditions of silica precipitation and using multiple reinforcementsteps, silicas may be produced having properties that make themespecially useful for reinforcing elastomeric composites. It has beensuggested that as precipitated silica is dried, the material shrinks;consequently, pore diameters are reduced, surface area is reduced, andthe void volume is reduced. It is further suggested that by sufficientlyreinforcing the silica prior to drying, a more open structure isobtained after drying. It has been found that using potassium silicateas a replacement for some or all of the sodium silicate can result inthe production of reinforced amorphous precipitated silica of lowersurface area (U.S. Pat. No. 5,605,950). While ‘sodium silicate’ is apreferred example, it is to be understood that any silicate can be usedand are well known in the art. The silicate can be of any form, such as,but not limited to, disilicates, metasilicates, or alkali metalsilicates, such as sodium silicate or potassium silicate. For instance,when sodium silicate is used, the silicate can have a SiO₂ to Na₂Oweight ratio of from about 2:1 to about 4:1 or from 3:1 to 3.7:1. The“acidifying” step can involve the use of one or more acids such asstrong inorganic acids as that term is understood in the art. Examplesof acids can be or include sulfuric acid, nitric acid, hydrochloricacid, e.g., concentrated sulfuric acid. Further examples include one ormore organic acids, such as, but not limited to, acetic acid, formicacid, or carbonic acid. In this process, a sediment, (e.g, at the bottomof a reaction vessel or tank) is formed. The sediment can include thesilicate and at least one electrolyte. The amount of silicate present inthe sediment may be either the total amount required for the reaction oronly a portion of that amount. The term “electrolyte” is any ionic ormolecular species which decomposes or dissociates when in solution, toform ions or charged particles. Examples of electrolytes include salts,such as alkali metal salts or alkaline earth metal salts. A particularexample is the salt of the starting material silicate and the acid, forexample sodium sulfate in the case of a reaction between a sodiumsilicate and sulfuric acid. The concentration of the electrolyte in theinitial sediment can be less than 17 g/l, such as less than 14 g/l. Theconcentration of silica in the initial sediment can be less than 100 gSiO₂ per liter, such as less than 80 g/l or less than 70 g/l. When theacid used for the neutralization is in a high concentration, especiallyover 70%, the reaction can be conducted using an initial silicatesediment in which the concentration of SiO₂ is less than 80 g/l. Thesecond stage of the process can include adding additional acid into thesediment having the composition described above. Addition of thisadditional acid, which results in a correlated lowering of the pH of thereaction medium, can continue until a pH of at least about 7, such asfrom 7 to 8, is attained. Once this value is attained and in the eventof an initial sediment having only a portion of the total amount ofsilicate required, the additional acid can be introduced with theremainder of the silicate simultaneously. The precipitation reaction isgenerally completed when all of the remaining silicate has been added.The next step can be allowing the reaction medium to mature (age) whenthe precipitation is complete, for example, maturing the reaction mediumfrom 5 minutes to 1 hour, or more. As an option, additional acid can beadded to the reaction medium after precipitation, optionally in a laterstage. The acid can be generally added until a pH of from 3 to 6.5 isreached, such as from 4 to 6.5 is attained. Addition of the acid permitsthe pH of the final product silica to be adjusted to a particular valuedesired. The temperature of the reaction medium can be from about 70° to98° C. The reaction can be carried out at a constant temperature rangingfrom 80° to 95° C. As an option, the temperature at the end of thereaction can be higher than at the beginning. For instance, thetemperature at the beginning of the reaction can be from 70° to 95° C.;and can then be increased to a range of from 80° to 98° C. andmaintained at that level to the end of the reaction. A silica, such as aprecipitated silica which is also sometimes described as a silica pulpis obtained after the reaction. The reaction product that contains thesilica can then be separated (e.g., a liquid/solid separation). Such aseparation can include a filtration, and optionally followed by washing.The filtration may be effected by any suitable technique, for examplevia a filter press or band filter, or rotating filter under vacuum. Thesuspension of precipitated silica thus recovered can be considered a“filter cake”. The proportion of dry solids in the suspension at thispoint is generally no greater than 24 wt %, based on the weight of thesuspension. As an option, the filter cake may be subjected to one ormore milling steps or operations. This may include transferring the cakeinto a colloidal or ball-type mill. One means for lowering the viscosityof the suspension entails the addition of aluminum thereto, particularlyin the form of sodium aluminate, at the stage of actual disintegration.Details of the formation of precipitated silica using an acid andsilicate and filtering step are for instance described in U.S. Pat. Nos.9,068,060, 7,250,463, 7,071,257, 6,013,234 5,605,950, and 5,403,570, allincorporated in their entirety by reference herein.

FIG. 3 provides a block diagram that provides options of how the silicathat is used to include or form the first fluid (which is then used, forinstance, in the process shown in FIG. 2) can be prepared. The boxesshown in dashed lines represent optional steps or processing of thesilica. The process(es) in FIG. 3 can be a batch process or continuousprocess or semi-continuous process. Various options are show in thediagram 200. For instance, a silicate solution 201 can be combined withan acid(s) 203 in a reactor 205. Silica in the form of precipitatedsilica can be obtained (recovered) 206, for instance in a recovery tank,tray or belt (not shown) along with an electrolyte such as a salt. As anoption, the silica 206 can optionally be subjected to a washing step(s)241 to remove at least a portion or most or all of the electrolyte ifdesired. With or without the optional washing step 241, at this point,the silica can be used per arrow/route 217 as the first fluid in thepresent application. As shown in FIG. 3, the silica from any of theoptions can be subjected to further processing as reflected in step 237.The further processing of the silica 237 can include, but is not limitedto, one or more of dilution (e.g., addition of water or aqueous fluid),destabilization (e.g, adding an acid and/or salt), ion exchange (e.g.,replacing Na and sulfate ions with, e.g., Ca and nitrate ions), and/ordiafiltration with or without water. Agitation and/or milling 231, as anoption can occur before and/or after the optional ‘further processing’step 237. Any number of ‘further processing’ steps can be used at thispoint. As a further option, the silica (in lieu of route 217), can besubjected to one or more of steps 207, 209, 211, and/or 225. Forinstance, the silica from reactor 205 can optionally be washed 241,and/or can be filter pressed (or subjected to one or more water removingprocesses/techniques) 207 and/or subjected to milling 209 and/ordirected to a wash/dilution tank 211 (where water or aqueous fluid 215can be provided to wash or dilute the silica) and/or subjected tomilling 213. As an option, the silica from any of the steps 207, 209,211, or 213 can be used per arrow/route 219, 221, 223, or 225 shown inFIG. 3. As with arrow/route 217, any of arrow/route 219, 221, 223, or225 can be subjected to further processing as reflected in step 237and/or step 231. One or more coupling agents can be added to the silicaat various stages of the flow diagram, 243, 245 and/or 247, shown inFIG. 3. As stated, the silica taken from one or more of theselocations/feeds 227 can optionally be agitated and/or subjected tomilling 231 to reduce silica particle agglomeration, control silicaparticle size distribution, fluidize the silica slurry, lower silicaslurry viscosity, and/or to obtain a better dispersion in liquid, and/orfurther processed per step 237, to for instance destabilize the silicain the slurry. As an example, the silica optionally taken from per route217 can have a solids content of from 2 wt % to 40 wt %. As an example,the silica optionally taken from location 219 can have a solids contentof from 10 wt % to 25 wt %. As an example, the silica optionally takenfrom location 221 can have a solids content of from 10 wt % to 40 wt %.As an example, the silica optionally taken from location 223 can have asolids content of from 2 wt % to 30 wt %. As an example, the silicaoptionally taken from location 225 can have a solids content of from 10wt % to 40 wt %. If needed, for any of the options, the addition ofwater or aqueous fluid 229 can be introduced to the silica feed 227 toraise the water content (reduce the solids content) for purposes offorming the first fluid of from about 6 wt % to 35 wt % silica.

In the method, a fluid that includes an elastomer latex and anadditional fluid that includes a destabilized dispersion of silicasupplied, for instance, as a jet under pressure are combined togetherunder continuous flow conditions and under selected volumetric flowrates, pressure, and velocities to rapidly and intimately mix the twofluids. The combining, for instance in a semi-confined space underpressure, is such that the silica is distributed throughout theelastomer latex and, in parallel, the elastomer latex is transformedfrom a liquid to a solid or semi-solid phase, i.e., a liquid to solidinversion, or coagulation, of the latex occurs, capturing thedistributed silica and water in the rubber and forming a solid orsemi-solid silica-containing continuous rubber phase in a continuous orsemi-continuous flow out of the reaction zone (e.g., from opening atoutlet (7) in FIGS. 1A-1C). At this point, the product can be consideredan elastomer composite of a continuous rubber phase containing silicaparticles, a silica-containing coherent rubber, or a silica elastomercomposite. It is believed that the silica particles first must bedistributed in the elastomer latex to obtain the desired product, andthe liquid to solid phase inversion follows immediately upon the silicadistribution. However, with the continuous and extremely rapid rate ofcombining the fluids (i.e., less than 2 seconds, less than 1 second,less than 0.5 second, less than 0.25 second, less than 0.1 second, or onthe order of milliseconds), and the energetic and intimate mixing ofrelatively small volumes of fluids in the reaction zone (e.g., fluidvolumes on the order of 10 to 500 cc), the parallel steps ofdistribution of the silica particles and liquid to solid phasetransformation of the elastomer latex can happen nearly simultaneously.The ‘reaction zone’ as used herein is the zone where the intimate mixingoccurs along with coagulation of the mixture. The mixture moves throughthe reaction zone and to outlet (7).

An exemplary method for preparing the elastomer composite involvessimultaneously feeding a first fluid comprising a destabilizeddispersion of silica and a second fluid comprising an elastomer latex(e.g. natural rubber latex) fluid to a reaction zone. The first fluidcomprising the destabilized dispersion of silica can be fed at a flowrate based on its volume, and the second fluid comprising the elastomerlatex can be fed at a flow rate based on its volume (i.e., volumetricflow rates). The volumetric flows of either the first fluid, the secondfluid, or both the first and second fluid can be adjusted or provided soas to yield an elastomer composite having a silica content of from 15 to180 parts per hundred weight rubber (phr) (e.g., from 35 to 180 phr,from 20 phr to 150 phr, from 25 phr to 125 phr, from 25 phr to 100 phr,from 35 to 115 phr, or from 40 phr to 115 phr, or from 40 phr to 90 phrand the like). The fluid that contains the destabilized dispersion ofsilica may be referred to as the first fluid in some embodiments herein.This fluid is a separate fluid from the fluid containing the elastomerlatex. Either fluid can be introduced through one inlet or injectionpoint or through more than one inlet or injection point.

The volumetric flow ratio of the first fluid (destabilized silicadispersion) to the second fluid (latex fluid) can be adjusted to permitthe desired elastomer composite to form. Examples of such volumetricflow ratios include, but are not limited to, a volumetric ratio of from0.4:1 (first fluid to second fluid) to 3.2:1; from 0.2:1 to 2:1 and thelike. The volumetric flow ratio between the first fluid and second fluidcan be adjusted by any means or technique. For instance, the volumetricflow rate of the first or second fluid or both can be adjusted by a)increasing the volumetric flow rate, b) decreasing the volumetric flowrate, and/or c) adjusting the flow rates of the fluids relative to eachother. Pressure created by physical constraints applied to the flow ofthe first fluid causes formation of a high velocity jet that enables thecombination of the destabilized silica dispersion with the elastomerlatex to occur rapidly, e.g., in a fraction of a second. As an example,the time during which two fluids are mixed and a liquid to solid phaseinversion occurs can be on the order of milliseconds (e.g., about 50 msto about 1500 ms or about 100 ms to about 1000 ms). For a givenselection of fluids, if the velocity of the first fluid is too slow toadequately mix the fluids, or the residence time is too short, then asolid rubber phase and solid product flow may not develop. If theduration of the process is too long, back pressure may develop in thereaction zone and the continuous flow of materials halted. Likewise, ifthe velocity of the first fluid is too fast, and the duration of theprocess is too short, a solid rubber phase and solid product flow maynot develop.

As described earlier, the relative volumetric flows of the first fluid(destabilized silica slurry) and the second fluid (latex) can beadjusted, and when at least one salt is used as the destabilizationagent, it is preferred to adjust the volumetric flow ratio ofdestabilized silica slurry to elastomer latex so as to be 0.4:1 to3.2:1. Other flow ratios may be used.

When at least one acid is used as the destabilization agent, it ispreferred to adjust the volumetric flow ratio of destabilized silicaslurry to elastomer latex so as to be 0.2:1 to 2:1. Other flow ratiosmay be used.

The elastomer latex can contain at least one base (such as ammonia), andthe destabilized dispersion of silica can be achieved with the additionof at least one acid, wherein the molar ratio of the acid in the firstfluid (silica) and the base (e.g., ammonia) in the second fluid (latex)is at least 1.0, or at least 1.1, or at least 1.2, such as from 1 to 2or 1.5 to 4.5. The base can be present in a variety of amounts in theelastomer latex, such as, but not limited to, 0.3 wt % to about 0.7 wt %(based on the total weight of the elastomer latex), or other amountsbelow or above this range.

The destabilized silica dispersion can be fed to the reaction zonepreferably as a continuous, high velocity, e.g., about 6 m/s to about250 m/s, or about 30 m/s to about 200 m/s, or about 10 m/s to about 150m/s, or about 6 m/s to about 200 m/s, jet of injected fluid, and thefluid containing the elastomer latex can be fed at a relatively lowervelocity, e.g., about 0.4 m/s to about 11 m/s, or about 0.4 m/s to about5 m/s, or about 1.9 m/s to about 11 m/s, or about 1 m/s to about 10 m/sor about 1 m/s to about 5 m/s. The velocities of the fluids are chosenfor optimizing mixing between fluids and fast coagulation of elastomerlatex. The velocity of the elastomer latex fed into the reaction zoneshould be preferably high enough to generate turbulent flow for bettermixing with destabilized silica slurry. Yet, the velocity of theelastomer latex should be kept low enough so that latex would notcoagulate from shear before it is well mixed with the destabilizedsilica slurry. In addition, the velocity of the elastomer latex shouldbe kept low enough before it enters into the reaction zone forpreventing clogging of latex supply lines from coagulation of latex dueto high shear. Similarly, there is also an optimized range of thevelocity of destabilized silica dispersion. It is theorized that if thevelocity of the destabilized silica slurry is too high, the rate ofshear induced agglomeration of silica particles could be too high toallow adequate, uniform mixing between silica particles and elastomerlatex particles.

Shear thickening from agglomeration and networking of silica particlesalso could reduce turbulence of the destabilized silica slurry andadversely affect the mixing between silica and latex. On the other hand,if the velocity of the destabilized silica slurry is too low, there maynot be sufficient mixing between silica particles and elastomer latexparticles. Preferably, at least one of the fluids entering into thereaction zone has a turbulent flow. In general, due to much higherviscosity of a typical destabilized silica dispersion relative to atypical elastomer latex, a much higher velocity of the destabilizedsilica dispersion is needed for generating good fluid dynamics formixing with the elastomer latex and fast coagulation of the latex. Suchhigh velocity flow of the destabilized silica dispersion may inducecavitation in the reaction zone to enhance rapid mixing of fluids anddistribution of silica particles in the elastomer latex. The velocity ofthe destabilized silica dispersion can be altered by using differentvolumetric flow rates, or a different nozzle or tip (3 a) (wider ornarrower in diameter) at the inlet (3) that feeds the first fluidcomprising destabilized silica dispersion. With use of a nozzle toincrease the velocity of the destabilized silica dispersion, it can beprovided under pressure ranging from about 30 psi to about 3,000 psi, orabout 30 psi to about 200 psi, or about 200 psi to about 3,000 psi, orabout 500 psi to about 2,000 psi or a relative pressure at least 2 timeshigher than the pressure applied to the fluid containing the elastomerlatex, or 2 to 100 times higher. The second fluid of elastomer latex canbe provided, as an example, at a pressure ranging from about 20 psi toabout 30 psi. The pressure in the first fluid supply system may be up toabout 500 psi.

Based on the production variables described herein, such as the velocityof the destabilized silica slurry fluid, the velocity of the latexfluid, the relative flow rates of the destabilized silica slurry andlatex fluids, the concentration of the destabilizing agent such as asalt and/or acid, the silica concentration in the destabilized slurry,the rubber weight percent in the latex, the ammonia concentration in thelatex, and/or the acid (if present) to ammonia ratio, it is possible tocontrol, obtain, and/or predict formation of a solid or semi-solidsilica-containing continuous rubber phase over a range of desired silicacontents. Thus, the process can be operated over an optimized range ofvariables. Thus, the a) velocity of one or both fluids, b) thevolumetric flow ratio of the fluids, c) the destabilized nature of thesilica, d) particulate silica concentration, e.g., 6 to 35 weightpercent, of the destabilized silica dispersion, and e) the dry rubbercontent, e.g., 10 to 70 weight percent, of the latex, can permit mixingunder high impact conditions so as to cause a liquid to solid inversionof the elastomer latex and uniformly disperse the silica in the latex ata selected silica to rubber ratio, and thus form a flow of a solid orsemi-solid silica-containing continuous rubber phase. The recovery ofthe flow of solid or semi-solid silica-containing continuous rubberphase can be achieved in any conventional technique for recovery of asolid or semi-solid flow of material. The recovery can permit the solidor semi-solid flow to enter into a container or tank or other holdingdevice. Such container or holding tank may contain a solution of salt oracid or both to effect further coagulation of the product to a moreelastic state. For example, the recovering can be transporting orpumping the solid flow to other processing areas or devices for furtherprocessing, of which some options are described herein. The recoveringcan be continuous, semi-continuous, or by batch. The outflow end of thereaction zone preferably is semi-confined and open to the atmosphere,and the flow of solid or semi-solid elastomer composite is preferablyrecovered at ambient pressure to allow continuous operation of theprocess.

The flow of a solid silica-containing continuous rubber phase can be inthe form of more or less elastic, rope-like “worms” or globules. Thesolid silica-containing continuous rubber phase may be capable of beingstretched to 130-150% of its original length without breaking. In othercases, a semi-solid silica-containing continuous rubber phase can be inthe form of non-elastic, viscous paste or gel-like material that candevelop elastic properties. In each case, the output is a coherent,flowing solid whose consistency can be highly elastic or slightlyelastic and viscous. The output from the reaction zone can be asubstantially constant flow concurrent with the on-going feeding of theelastomer latex and the destabilized dispersion of silica fluids intothe reaction zone. Steps in the process, such as the preparation of thefluids, may be done as continuous, semi-continuous, or batch operations.The resulting solid or semi-solid silica-containing continuous rubberphase can be subjected to subsequent further processing steps, includingcontinuous, semi-continuous, or batch operations.

The solid or semi-solid silica-containing continuous rubber phasecreated in the process contains water, or other aqueous fluid, andsolutes from the original fluids, and, for instance, can contain fromabout 40 wt % to about 95 wt % water, or 40 wt % to about 90 wt % water,or from about 45 wt % to about 90 wt % water, or from about 50 to about85 wt % water content, or from about 60 to about 80 wt % water, based onthe total weight of the flow of silica elastomer composite. As anoption, after forming the solid or semi-solid silica-containing rubberphase comprising such water contents, this product can be subjected tosuitable de-watering and masticating steps and compounding steps todevelop desired rubber properties and fabricate rubber compounds.Further details of the process and other post-processing steps are setforth below and can be used in any embodiment of the present invention.

A semi-solid silica-containing continuous rubber phase may be convertedto a solid silica-containing continuous rubber phase. This for instancecan be done by subjecting the semi-solid silica-containing continuousrubber phase to mechanical steps that remove water from the compositeand/or having the semi-solid material sit for a time (e.g., afterrecovery from the reaction zone in an offline location) for instance, 10minutes to 24 hours or more; and/or heating the semi-solidsilica-containing continuous rubber phase to remove water content (e.g.,a temperature of from about 50° C. to about 200° C.); and/or subjectingthe semi-solid material to acid or additional acid such as in an acidbath, or to salt or additional salt, or a salt bath, or to a combinationof acid and salt, and the like. One or more or all of these steps can beused. In fact, one or more or all of steps can be used as a furtherprocessing step(s) even when a solid silica-containing continuous rubberphase is initially or subsequently recovered.

The degree of destabilization of the silica slurry, at least in part,determines the amount of silica that can be present in the silicaelastomer composite (e.g., captured and distributed uniformly within thecomposite) for a given silica concentration in the silica slurry and agiven dry rubber content of the latex. At lower selected target silicato rubber ratios (e.g., 15 phr to 45 phr), the concentration ofdestabilizing agent may not be high enough in the silica slurry andultimately the silica/latex mixture to rapidly coagulate and form asolid or semi-solid silica-containing continuous rubber phase. Inaddition, selecting appropriate silica and rubber concentrations andappropriate relative fluid flow rates as described herein areconsiderations for forming the solid or semi-solid product. For example,at relatively low volumetric flow ratios of destabilized slurry tolatex, the amount of the destabilizing agent in the destabilized silicaslurry may not be sufficient to facilitate rapid coagulation ofelastomer latex in the reaction zone. Generally, for a given elastomerlatex, lower silica loadings can be achieved by increasing thedestabilization of the silica slurry and/or reducing the weightpercentage of silica in the destabilized slurry.

When a dispersion of silica is destabilized, the silica particles tendto flocculate. When a dispersion of silica is too highly destabilized,the silica can ‘fall out’ of solution and become unsuited for use inpreferred embodiments.

When destabilization occurs, the surface charges on the silica aretypically not completely removed. However, sometimes when the silicaparticle, or the silica dispersion, is treated to destabilize, theisoelectric point (IEP) may be crossed over from a negative zetapotential to a positive zeta potential value. Generally for silica, thenet charge on the surface of the silica particles is reduced and themagnitude of the zeta potential is decreased during destabilization.

For higher silica to rubber ratios in the silica elastomer composite,one may select higher silica concentrations in the destabilized slurryand/or a higher silica fluid to latex fluid volumetric flow ratio. Oncethe silica slurry is destabilized and initially combined with the latexfluid, if the mixture does not coagulate, the volume flow ratio of thefirst fluid and second fluid can be adjusted, such as by decreasing thevolume flow of latex, which effectively provides a higher silica torubber ratio in the elastomer composite. In this step of adjusting theamount of latex present, the amount of latex is, or becomes, an amountthat does not cause excessive dilution of the concentration of thedestabilizing agent in the overall mixture such that the desired productcan be formed within the residence time in the reaction zone. To obtaina desired silica to rubber ratio in the elastomer composite, variousoptions are available. As an option, the level of destabilization of thesilica slurry can be increased, such as by reducing the magnitude of thezeta potential of the destabilized silica slurry (e.g., by adding moresalt and/or acid). Or, as an option, the silica concentration in thedestabilized silica slurry can be adjusted, for instance, by lowering orincreasing the silica concentration in the destabilized silica slurry.Or, as an option, a latex can be used that has a higher rubber content,or a latex can be diluted to a lower rubber content, or the relativeflow rate of the latex can be increased. Or, as an option, the flow rateand orifice size (where each can control or affect velocity of thefluid(s)) or relative orientation of the two fluid flows can be modifiedto shorten or lengthen the residence time of the combined fluids in thereaction zone, and/or alter the amount and type of turbulence at thepoint of impact of the first fluid on the second fluid. Any one or twoor more of these options can be used to adjust the process parametersand obtain a target or desired silica to rubber ratio in the elastomercomposite.

The amount or level of destabilization of the silica slurry is a majorfactor in determining what silica to rubber ratio can be achieved in thesilica elastomer composite. A destabilizing agent used to destabilizesilica in the slurry may play a role in accelerating coagulation ofelastomer latex particles when the destabilized silica slurry is mixedwith elastomer latex in the reaction zone. It is theorized that the rateof latex coagulation in the reaction zone may depend on theconcentration of the destabilizing agent in the combined fluids. It hasbeen observed that by running the process for producing silica elastomercomposite under various conditions, one may determine a thresholdconcentration of a destabilizing agent present in the combined mixtureof fluids at the time of mixing that is effective to produce solid orsemi-solid silica-containing continuous rubber phase. An example ofselecting and adjusting process conditions to achieve the thresholdconcentration to yield solid or semi-solid silica-containing continuousrubber phase, is described in the Examples below. If the thresholdconcentration for a given selection and composition of fluids,volumetric flows, and velocities is not equaled or exceeded, a solid orsemi-solid silica-containing continuous rubber phase will generally notbe produced.

The minimum amount of destabilization of the silica slurry is indicatedby a zeta potential magnitude of less than 30 mV (e.g. with zetapotentials such as −29.9 mV to about 29.9 mV, about −28 mV to about 20mV, about −27 mV to about 10 mV, about −27 mV to about 0 mV, about −25mV to about 0 mV, about −20 mV to about 0 mV, about −15 mV to about 0mV, about −10 mV to about 0 mV and the like). If the silica slurry hasbeen destabilized to within this zeta potential range, then the silicain the destabilized slurry can be incorporated into a solid orsemi-solid silica-containing continuous rubber phase when combined withthe elastomer latex.

While it may be desirable to destabilize the latex before combining itwith the silica slurry, under shear conditions such as those presentwhile continuously pumping the latex into the reaction zone, it isdifficult to destabilize the latex fluid beforehand without causingpremature coagulation of the latex. However, the destabilization agentused in the destabilized silica slurry may be present in a surplusamount to enhance destabilization of the latex, and/or mitigate dilutionof the agent once the destabilized silica slurry and latex fluid arecombined. As a further option, at especially high silica concentrations(e.g., >25 wt % silica in the silica slurry), some added destabilizationagent can be added separately to the mixture of the destabilized silicaslurry and elastomer latex in the reaction zone to enhance coagulationof the latex.

Without wishing to be bound to any theory, the process for producingsilica elastomer composite is believed to form interpenetrated coherentnetworks of both rubber particles and silica aggregates in about twoseconds or less, such as a fraction of a second, as the two fluidscombine and the phase inversion occurs, resulting in a solid orsemi-solid material comprising these networks with encapsulated water.Such fast network formation allows the continuous production of a solidor semi-solid silica-containing continuous rubber phase. It is theorizedthat shear induced agglomeration of silica particles as the destabilizedsilica slurry passes through an inlet nozzle to be combined with theelastomer latex may be useful for creating unique, uniform particlearrangement in rubber masterbatches and capturing silica particleswithin rubber through hetero-coagulation between silica and rubberparticles. It is further theorized that without such an interpenetratednetwork, there may not be a composite of a solid or semi-sold,continuous rubber phase containing dispersed silica particles, in theshape of a worm, or solid pieces, for instance, that encapsulates 40-95wt % water and retains all or most of the silica in subsequentdewatering processes including squeezing and high energy mechanicalworking.

It is theorized that the formation of a silica network arises, at leastin part, from shear induced silica particle agglomeration as thedestabilized silica slurry passes through a pressurized nozzle (3 a) athigh velocity through the first inlet (3) into the reaction zone (13),as shown in FIGS. 1A-1C. This process is facilitated by reduction ofstability of silica in the destabilized slurry when the silica slurryhas been destabilized (e.g., by treating the silica slurry with salt oracid or both).

It is theorized that the liquid to solid phase inversion of the latexmay result from various factors, including shear induced coagulationfrom mixing with the high velocity jet of destabilized silica slurry,interaction of the silica surface with the latex components, ionic orchemical coagulation from contact with the silica slurry containingdestabilizing agent, and a combination of these factors. In order toform composite material comprising the interpenetrated silica networkand rubber network, the rates of each network formation as well as therate of mixing should be balanced. For example, for highly destabilizedsilica slurries at a high salt concentration in the slurry,agglomeration and network formation of silica particles occurs rapidlyunder shear conditions. In this case, volumetric flows and velocitiesare set so the latex has a rapid rate of coagulation for formation ofthe interpenetrated silica/rubber networks. Rates of formation areslower with more lightly destabilized silica slurries.

One exemplary process to produce a silica elastomer composite includesfeeding a continuous flow of a fluid that contains at least elastomerlatex (sometimes referred to as the second fluid) through inlet 11(FIGS. 1A, 1B, and/or 1C), to a reaction zone 13 at a volumetric flowrate of about 20 L/hr to about 1900 L/hr. The method further includesfeeding a continuous flow of a further fluid containing a destabilizeddispersion of silica through inlet 3 (sometimes referred to as the firstfluid) under pressure that can be accomplished by way of nozzle tips (inFIG. 1A-1C, at 3 a) at a volumetric flow rate of 30 L/hr to 1700 L/hr.The destabilized state of the silica dispersion and the impacting of thetwo fluid flows (introduced at inlets 3 and 11) under high energyconditions created by introducing the first fluid as a high velocity jet(e.g., about 6 m/s to about 250 m/s) that impacts the lower velocitylatex flow (e.g., 0.4-11 m/s) entering the reaction zone at an angleapproximately perpendicular to the high speed jet of the first fluid iseffective to intimately mix the silica with the latex flow, promoting auniform distribution of silica in the flow of solid silica-containingcontinuous rubber phase from the outlet of the reaction zone.

As an option, the elastomer latex introduced, for instance, throughinlet 11 can be a blend of two or more latexes, such as a blend of twoor more synthetic latexes. As an option, the devices in FIGS. 1A, 1B,and/or 1C can be modified to have one or more additional inlets so as tointroduce other components to the reaction zone, such as one or moreadditional latexes. For instance, in FIG. 1C, inlet 14 can be used tointroduce a further latex besides using inlet 11. The one or moreadditional inlets can be sequential to each other, or be adjacent toeach other or set forth in any orientation as long as the material (e.g.latex) being introduced through the inlet(s) has sufficient time todisperse or be incorporated into the resulting flow. In WO 2011/034587,incorporated in its entirety by reference herein, FIGS. 1, 2A, and 2Bprovide examples of additional inlets and their orientations which canbe adopted here for use with embodiments of the present invention. As aparticular example, one inlet can introduce a flow that includes naturalrubber latex and an additional inlet can introduce a synthetic elastomerlatex, and these latex flows are combined with the flow of thedestabilized dispersion of silica to result in the flow of a solid orsemi-solid silica-containing continuous rubber phase. When more than oneinlet is utilized for elastomer latex introduction, the flow rates canbe the same or different from each other.

FIG. 2 sets forth an example, using a block diagram of various stepsthat can occur in the formation of the elastomer composite. As shown inFIG. 2, the destabilized dispersion of silica (first fluid) 100 isintroduced into the reaction zone 103 and the fluid containing theelastomer latex (second fluid) 105 is introduced also into the reactionzone 103. As an option, a flow of solid or semi-solid silica-containingcontinuous rubber phase exits the reaction zone 103 and can optionallyenter a holding zone 116 (e.g., a holding tank, with or without theaddition of a salt or acid solution to further enhance coagulation ofrubber and formation of silica/rubber networks); and can optionallyenter, directly, or after diversion to a holding zone 116, a dewateringzone 105; can optionally enter a continuous mixer/compounder 107; canoptionally enter a mill (e.g., open mill, also called a roll mill) 109;can be subjected to additional extra milling 111 (same or differentconditions as mill 109) (such as same or different energy input); can besubjected to optional mixing by mixer 115, and/or can be granulatedusing a granulator 117, and then can optionally be baled, using a baler119, and can optionally be broken down by use of an additional mixer121.

With regard to the silica, one or more types of silica, or anycombination of silica(s), can be used in any embodiment of the presentinvention. The silica suitable for reinforcing elastomer composites canbe characterized by a surface area (BET) of about 20 m²/g to about 450m²/g; about 30 m²/g to about 450 m²/g; about 30 m²/g to about 400 m²/g;or about 60 m²/g to about 250 m²/g; and for heavy vehicle tire treads aBET surface area of about 60 m²/g to about 250 m²/g or for example fromabout 80 m²/g to about 200 m²/g. Highly dispersible precipitated silicacan be used as the filler in the present methods. Highly dispersibleprecipitated silica (“HDS”) is understood to mean any silica having asubstantial ability to dis-agglomerate and disperse in an elastomericmatrix. Such determinations may be observed in known manner by electronor optical microscopy on thin sections of elastomer composite. Examplesof commercial grades of HDS include, Perkasil® GT 3000GRAN silica fromWR Grace & Co, Ultrasil® 7000 silica from Evonik Industries, Zeosil®1165 MP and 1115 MP silica from Solvay S.A., Hi-Sil® EZ 160G silica fromPPG Industries, Inc., and Zeopol® 8741 or 8745 silica from JM HuberCorporation. Conventional non-HDS precipitated silica may be used aswell. Examples of commercial grades of conventional precipitated silicainclude, Perkasil® KS 408 silica from WR Grace & Co, Zeosil® 175GRsilica from Solvay S.A., Ultrasil® VN3 silica from Evonik Industries,Hi-Sil® 243 silica from PPG Industries, Inc. and the Hubersil® 161silica from JM Huber Corporation. Hydrophobic precipitated silica withsurface attached silane coupling agents may also be used. Examples ofcommercial grades of hydrophobic precipitated silica include Agilon®400,454, or 458 silica from PPG Industries, Inc. and Coupsil silicas fromEvonik Industries, for example Coupsil 6109 silica.

Typically the silica (e.g., silica particles) have a silica content ofat least 20 wt %, at least 25 wt %, at least 30 wt %, at least 35 wt %,at least 40 wt %, at least 50 wt %, at least 60 wt %, at least 70 wt %,at least 80 wt %, at least 90 wt %, or almost 100 wt % or 100 wt %, orfrom about 20 wt % to about 100 wt %, all based on the total weight ofthe particle. Any of the silica(s) can be chemically functionalized,such as to have attached or adsorbed chemical groups, such as attachedor adsorbed organic groups. Any combination of silica(s) can be used.The silica that forms the silica slurry and/or destabilized silicaslurry can be in part or entirely a silica having a hydrophobic surface,which can be a silica that is hydrophobic or a silica that becomeshydrophobic by rendering the surface of the silica hydrophobic bytreatment (e.g., chemical treatment). The hydrophobic surface may beobtained by chemically modifying the silica particle with hydrophobizingsilanes without ionic groups, e.g.,bis-triethoxysilylpropyltetrasulfide. Such a surface reaction on silicamay be carried out in a separate process step before dispersion, orperformed in-situ in a silica dispersion. The surface reaction reducessilanol density on the silica surface, thus reducing ionic chargedensity of the silica particle in the slurry. Suitable hydrophobicsurface-treated silica particles for use in dispersions may be obtainedfrom commercial sources, such as Agilon® 454 silica and Agilon® 400silica, from PPG Industries. Silica dispersions and destabilized silicadispersions may be made using silica particles having low surfacesilanol density. Such silica may be obtained through dehydroxylation attemperatures over 150° C. via, for example, a calcination process.

Further, the silica slurry and/or destabilized silica slurry cancontain, as an option, a minor amount (10 wt % or less, based on a totalweight of particulate material) of any non-silica particles, such ascarbon black(s) or zinc oxide, or calcium carbonate, or otherparticulate materials useful in rubber compositions (e.g., 95 wt %precipitated silica and 5 wt % carbon black). Any reinforcing ornon-reinforcing grade of carbon black may be selected to yield thedesired property in the final rubber composition.

Silica may be dispersed in aqueous fluid according to any techniqueknown to those of skill in the art. A dispersion of particulate silicacan be subjected to mechanical processing, for instance, to reduceparticle size. This can be done prior to or during or afterdestabilizing of the dispersion and can contribute in a minor way ormajor way to the destabilizing of the dispersion. The mechanicalprocessing can comprise or include grinding, milling, comminution,bashing, or high shear fluid processing, or any combinations thereof.

For example, a silica slurry can be made by dispersing silica in a fluidby means of a grinding process. Such a grinding process reduces the sizeof most silica agglomerates (e.g. over 80% by volume) in the fluid tobelow 10 microns, and preferably below 1 micron, the typical size rangeof colloidal particles. The fluid may be water, an aqueous fluid, or anon-aqueous polar fluid. The slurry, for instance, may comprise fromabout 6 wt % to about 35 wt % silica-containing particles, based on theweight of the slurry. The size of silica particles may be determinedusing a light scattering technique. Such a slurry when made in waterusing silica particles having low residual salt content at a pH of 6-8,typically has a zeta potential magnitude higher than, or equal to, 30 mVand shows good stability against aggregation, gelling, and settlement ina storage tank with slow stirring (e.g. stirring speed below 60 RPM). Aswell-ground silica particles are generally stable in water at a pH ofaround 7 due to high negative charges on silica, very high shear isgenerally needed to overcome the repulsive energy barrier betweenparticles to induce particle agglomeration.

In an exemplary method employing silica, such as HDS granules, thesilica can be combined with water, and the resulting mixture is passedthrough a colloid mill, pipeline grinder, or the like to form adispersion fluid. This fluid is then passed to a homogenizer that morefinely disperses the filler in the carrier liquid to form the slurry.Exemplary homogenizers include, but are not limited to, theMicrofluidizer® system commercially available from MicrofluidicsInternational Corporation (Newton, Mass., USA). Also suitable arehomogenizers such as models MS18, MS45 and MC120, and serieshomogenizers available from the APV Homogenizer Division of APV Gaulin,Inc. (Wilmington, Mass., USA). Other suitable homogenizers arecommercially available and will be apparent to those skilled in the artgiven the benefit of the present disclosure. The optimal operatingpressure across a homogenizer may depend on the actual apparatus, thesilica type, and/or the silica content. As an example, a homogenizer maybe operated at a pressure of from about 10 psi to about 5000 psi orhigher, for example, from about 10 psi to about 1000 psi, about 1000 psito about 1700 psi, about 1700 psi to about 2200 psi, about 2200 psi toabout 2700 psi, about 2700 psi to about 3300 psi, about 3300 psi toabout 3800 psi, about 3800 psi to about 4300 psi, or about 4300 psi toabout 5000 psi. As indicated earlier, the dispersion of particulatesilica is destabilized before carrying out the masterbatch process, andthe dispersion can be destabilized by following one of the techniquesmentioned herein, before, during, or after any grinding or similarmechanical process.

Depending on the wet masterbatch method employed, a high silicaconcentration in slurry may be used to reduce the task of removingexcess water or other carrier. For the destabilized dispersion of silicaparticles, the liquid used can be water or other aqueous fluid or otherfluid. For the destabilized dispersion, from about 6 weight percent toabout 35 weight percent filler may be employed, for example, from about6 weight percent to about 9 weight percent, from about 9 weight percentto about 12 weight percent, from about 12 weight percent to about 16weight percent, from about 10 weight percent to about 28 weight percent,from about 16 weight percent to about 20 weight percent, from about 20weight percent to about 24 weight percent, from about 24 weight percentto about 28 weight percent, or from about 28 weight percent to about 30weight percent, based on the weight of the destabilized dispersion. Forthe destabilized dispersion, a higher silica concentration can havebenefits. For instance, silica concentration in the destabilized slurrycan be at least 10 weight percent or at least 15 weight percent, basedon the weight of the slurry (e.g., about 12 wt % to about 35 wt % orabout 15.1 wt % to about 35 wt %, or about 20 wt % to about 35 wt %),which can provide benefits such as, but not limited to, reducedwastewater, increased production rates, and/or reduction of theequipment size needed for the process. Those skilled in the art willrecognize, given the benefit of this disclosure, that the silicaconcentration (in weight percent) of the silica slurry (and in thedestabilized silica slurry) should be coordinated with other processvariables during the wet process to achieve a desired silica to rubberratio (in phr) in the ultimate product.

Details of a dispersion of silica are further described below. Ingeneral, a dispersion can be a material comprising more than one phasewhere at least one of the phases contains or includes or consists offinely divided phase domains, optionally in the colloidal size range,dispersed throughout a continuous phase. A dispersion or slurry ofsilica or silica dispersion can be prepared as a stable suspension ofparticulate silica in aqueous fluid, wherein the charge at the surfaceof the particles prevents particle agglomeration and the dispersion ischaracterized by a zeta potential magnitude of greater than or equal to30 mV. In such dispersions, the silica particles remain in stabledispersion, and/or suspension, with respect to aggregation andcoalescence, for instance, for at least 8 hours. A stable dispersion canbe one where constant particle size is maintained, and wherein theparticles do not settle or gel, or take a very long time to settleappreciably in the presence of slow or periodic stirring, for example,not settling appreciably after 8 hours, or 12 hours or 24 hours, or 48hours. For instance, for colloidal silica particles well dispersed inaqueous fluid, stability can generally be observed from a pH of 8 to 10.Further, with slow stirring of the dispersion, the silica particlesremain suspended in the fluid by means of particle surface charge,particle surface polarity, pH, selected particle concentration, particlesurface treatment, and combinations thereof. The fluid may be or includewater, an aqueous mixture, or a water miscible or partially misciblefluid, such as various alcohols, ethers, and other low molecular weightwater-miscible solvents, preferably having C₁-C₅ organic groups (e.g.,ethanol, methanol, propanol, ethyl ether, acetone, and the like). Asindicated above, the dispersion, for instance, may comprise about 6 wt %to about 35 wt %, about 10 wt % to about 28 wt %, about 12 wt % to about25 wt %, or about 15 wt % to about 30 wt % silica-containing particles,based on the weight of the dispersion.

A stable dispersion may be a colloidal dispersion. In general, acolloidal dispersion or colloid can be a substance where dispersedparticles are suspended throughout another substance. Thedispersed-phase particles have a diameter of from approximately about 1nanometer to about 1000 nanometers, and typically about 100 nanometersto about 500 nanometers. In a stable colloidal dispersion, particlesize, density, and concentration are such that gravity does not causeparticles to settle out of dispersion easily. Colloids with themagnitude of zeta potential of 30 mV or over are generally regarded asstable colloidal systems. Reduction of particle stability (e.g., silica)in a colloid or dispersion due to charge stabilization can be measuredby reduction of magnitude of zeta potential. Particle size may bemeasured by a light scattering method.

A destabilized silica dispersion can be understood to be a dispersion ofsilica in a fluid wherein weakened particle-to-particle repulsive forcesallow clustering of particles and formation of a silicaparticle-to-particle network or gel once the destabilized dispersion issubjected to an effective amount of shear. In certain cases, mechanicalshear may cause destabilization of silica dispersions and clustering ofsilica particles. The higher the degree of destabilization of silicaslurry, the lower the shear needed for aggregation of particles, and thehigher the rate of particle aggregation. For a destabilized dispersion,the dispersion can comprise from about 6 wt % to about 35 wt %particulate silica (based on the weight of the dispersion), e.g., fromabout 8 wt % to about 35 wt %, from about 10 wt % to about 28 wt %, fromabout 12 wt % to about 25 wt %, from about 15 wt % to about 30 wt %. Theaqueous fluid in the destabilized dispersion of silica particles may beor include water, an aqueous mixture, or a water miscible or partiallymiscible fluid, such as various alcohols, ethers, and other lowmolecular weight water-miscible solvents, preferably having C₁-C₅organic groups (e.g., ethanol, methanol, propanol, ethyl ether, acetone,and the like). To form silica elastomer composites, the stability ofsilica particles in a slurry or dispersion is reduced (i.e.,destabilized) by lowering the electrostatic energy barrier betweenparticles using an effective amount of a destabilizing agent such asacid or salt or both before the slurry is mixed with latex. Adestabilizing agent may be selected for its capacity to reduce repulsivecharge interaction among particle surfaces that prevent particles fromagglomeration in the fluid.

A destabilized dispersion of silica may be obtained by lowering the pHof the dispersion of silica to close to the isoelectric point of thesilica (around pH 2 for typical hydrophilic silicas). For example,destabilizing silica can be achieved by adding acid to lower a pH of thedispersion of particulate silica to 2 to 4, thus reducing the magnitudeof the zeta potential of the dispersion to less than 30 mV, such asbelow about 28 mV (e.g., zeta potentials of magnitude of about 18 mV toabout 6 mV for formic acid as the destabilization agent). The additionof acid and/or salt into silica slurry can effectively reduce thestability of silica particles dispersed in water. The acid or salt molarconcentration is generally the dominant factor that determines the zetapotential of the destabilized silica slurry. In general, a sufficientamount of acid or salt or both can be used to reduce the magnitude ofthe zeta potential of the silica slurry to less than 30 mV, such as 28mV or less, preferably 25 mV or less, for producing a semi-solid orsolid silica-containing continuous rubber phase.

The amount of acid used to destabilize the silica dispersion can be anamount to obtain a zeta potential magnitude in the destabilizeddispersion of less than 30 mV, such as 28 mV or less, or 25 mV or lower.The acid can be at least one organic or inorganic acid. The acid can beor include acetic acid, formic acid, citric acid, phosphoric acid, orsulfuric acid, or any combinations thereof. The acid can be or include aC_(i) to C₄ alkyl containing acid. The acid can be or include one thathas a molecular weight or a weight average molecular weight below 200,such as below 100 MW, or below 75 MW, or from about 25 MW to about 100MW. The amount of acid can vary and depend on the silica dispersionbeing destabilized. The amount of acid can be, for instance, from about0.8 wt % to about 7.5 wt %, for example, from about 1.5 wt % to about7.5 wt % or more (based on the total weight of the fluid comprising thedispersion of silica). If an acid is the only destabilizing agent used,the amount of acid can be an amount that lowers the pH of the dispersionof silica by at least 2 pH units, or to at least a pH of 5 or lower, orthe pKa range of the acid or acids in use, so as to reduce chargeinteractions among particles.

A destabilized dispersion may be obtained by treating a dispersion ofsilica with a destabilizing agent comprising one or more salts to alterslurry zeta potential to the range described above. The salt can be orinclude at least one metal salt (e.g., from Group 1, 2, or 13 metals).The salt can be or include a calcium salt, magnesium salt, or aluminumsalt. Exemplary counterions include nitrate, acetate, sulfate, halogenions such as chloride, bromide, iodine, and the like. The amount of saltcan be, for instance, from about 0.2 wt % to about 2 wt % or more, forexample, from about 0.5 or 1 wt % to about 1.6 wt % (based on the weightof the fluid comprising the destabilized dispersion of silica).

A combination of at least one salt and/or at least one acid can be usedto destabilize the dispersion of the silica.

When the destabilized dispersion of silica is achieved with the additionof at least one salt, the salt concentration in the destabilizeddispersion of silica can be from about 10 mM to about 160 mM, or otheramounts above or below this range.

When the destabilized dispersion of silica is achieved with the additionof at least one acid, the acid concentration in the destabilizeddispersion can be from about 200 mM to about 1000 mM, for example, about340 mM to about 1000 mM, or other amounts above or below this range.

A destabilized silica dispersion may be made using silica particlestreated to comprise an appropriate amount of surface functional groupscarrying positive charges so that the net charges on the silica surfaceare reduced sufficiently to decrease the magnitude of zeta potential ofthe dispersion below 30 mV. The net charge on the silica surface can bepositive, instead of negative, as a result of such surface treatment.The positively charged functional group may be introduced to silicasurface through chemical attachment or physical adsorption. For example,the silica surface may be treated withN-trimethoxylsilylpropyl-N,N,N-trimethylammonium chloride either beforeor after preparation of the silica dispersion. It is also possible toadsorb cationic coating agents, such as amine containing molecules andbasic amino acids on the silica surface. It is theorized that a netpositive charge on silica particle surfaces may enhance coagulation ofthe latex, which comprises negatively charged rubber particles, by meansof heterocoagulation.

With regard to the “second fluid,” which contains at least one elastomerlatex, this fluid may contain one or more elastomer latices. Anelastomer latex can be considered a stable colloidal dispersion ofrubber and may contain, for example, from about 10 wt % to about 70 wt %rubber based on the total weight of the latex. The rubber can bedispersed in a fluid, such as water or other aqueous fluid, for example.The aqueous content of this fluid (or water content) can be 40 wt % orhigher, such as 50 wt % or higher, or 60 wt % or higher, or 70 wt % orhigher, for instance from about 40 wt % to 90 wt % based on the weightof the fluid comprising the at least one elastomer latex. Suitableelastomer latices include both natural and synthetic elastomer laticesand latex blends. For example, elastomer latex may be made syntheticallyby polymerizing a monomer such as styrene that has been emulsified withsurfactants. The latex should be appropriate for the wet masterbatchprocess selected and the intended purpose or application of the finalrubber product. It will be within the ability of those skilled in theart to select suitable elastomer latex or a suitable blend of elastomerlatices for use in the methods and apparatus disclosed here, given thebenefit of this disclosure.

The elastomer latex can be or include natural rubber, such as anemulsion of natural rubber. Exemplary natural rubber latices include,but are not limited to, field latex, latex concentrate (produced, forexample, by evaporation, centrifugation or creaming), skim latex (e.g.,the supernatant remaining after production of latex concentrate bycentrifugation) and blends of any two or more of these in anyproportion. Natural rubber latex typically is treated with ammonia topreserve it, and the pH of treated latex typically ranges from 9 to 11.The ammonia content of the natural rubber latex may be adjusted, and canbe reduced, e.g., by bubbling nitrogen across or through the latex.Typically, latex suppliers desludge the latex by addition of diammoniumphosphate. They may also stabilize the latex by addition of ammoniumlaurate. The natural rubber latex may be diluted to a desired dry rubbercontent (DRC). Thus, the latex that can be used here can be a desludgedlatex. A secondary preservative, a mixture of tetramethylthiuramdisulfide and zinc oxide (TZ solution) may also be included. The latexshould be appropriate for the wet masterbatch process selected and theintended purpose or application of the final rubber product. The latexis provided typically in an aqueous carrier liquid (e.g, water). Theamount of the aqueous carrier liquid can vary, and for instance be fromabout 30 wt % to about 90 wt % based on the weight of the fluid. Inother words, such natural rubber latices may contain, or may be adjustedto contain, e.g., about 10 wt % to about 70 wt % rubber. Selection of asuitable latex or blend of latices will be well within the ability ofthose skilled in the art given the benefit of the present disclosure andthe knowledge of selection criteria generally well recognized in theindustry.

The natural rubber latex may also be chemically modified in some manner.For example, it may be treated to chemically or enzymatically modify orreduce various non-rubber components, or the rubber molecules themselvesmay be modified with various monomers or other chemical groups such aschlorine. Epoxidized natural rubber latex may be especially beneficialbecause the epoxidized rubber is believed to interact with the silicasurface (Martin, et al., Rubber Chemistry and Technology, May 2015,doi:10.5254/rct15.85940). Exemplary methods of chemically modifyingnatural rubber latex are described in European Patent Publications Nos.1489102, 1816144, and 1834980, Japanese Patent Publications Nos.2006152211, 2006152212, 2006169483, 2006183036, 2006213878, 2006213879,2007154089, and 2007154095, Great Britain Patent No. GB2113692, U.S.Pat. Nos. 6,841,606 and 7,312,271, and U.S. Patent Publication No.2005-0148723. Other methods known to those of skill in the art may beemployed as well.

Other exemplary elastomers include, but are not limited to, rubbers,polymers (e.g., homopolymers, copolymers and/or terpolymers) of1,3-butadiene, styrene, isoprene, isobutylene,2,3-dialkyl-1,3-butadiene, where alkyl may be methyl, ethyl, propyl,etc., acrylonitrile, ethylene, propylene and the like. The elastomer mayhave a glass transition temperature (Tg), as measured by differentialscanning calorimetry (DSC), ranging from about −120° C. to about 0° C.Examples include, but are not limited to, styrene-butadiene rubber(SBR), natural rubber and its derivatives such as chlorinated rubber,polybutadiene, polyisoprene, poly(styrene-co-butadiene) and the oilextended derivatives of any of them. Blends of any of the foregoing mayalso be used. The latex may be in an aqueous carrier liquid. Particularsuitable synthetic rubbers include: copolymers of styrene and butadienecomprising from about 10 percent by weight to about 70 percent by weightof styrene and from about 90 to about 30 percent by weight of butadienesuch as a copolymer of 19 parts styrene and 81 parts butadiene, acopolymer of 30 parts styrene and 70 parts butadiene, a copolymer of 43parts styrene and 57 parts butadiene and a copolymer of 50 parts styreneand 50 parts butadiene; polymers and copolymers of conjugated dienessuch as polybutadiene, polyisoprene, polychloroprene, and the like, andcopolymers of such conjugated dienes with an ethylenic group-containingmonomer copolymerizable therewith such as styrene, methyl styrene,chlorostyrene, acrylonitrile, 2-vinyl-pyridine,5-methyl-2-vinylpyridine, 5-ethyl-2-vinylpyridine,2-methyl-5-vinylpyridine, allyl-substituted acrylates, vinyl ketone,methyl isopropenyl ketone, methyl vinyl either, alpha-methylenecarboxylic acids and the esters and amides thereof, such as acrylic acidand dialkylacrylic acid amide. Also suitable for use herein arecopolymers of ethylene and other high alpha olefins such as propylene,1-butene, and 1-pentene. Blends of two or more types of elastomer latex,including blends of synthetic and natural rubber latex or with two ormore types of synthetic or natural rubber, may be used as well.

The rubber compositions can contain, in addition to the elastomer andfiller and coupling agent, various processing aids, oil extenders,antidegradants, antioxidants, and/or other additives.

The amount of silica (in parts per hundred of rubber, or phr) present inthe elastomer composite can be from about 15 phr to about 180 phr, about20 phr to about 150 phr, about 25 phr to about 80 phr, about 35 phr toabout 115 phr, about 35 phr to about 100 phr, about 40 phr to about 100phr, about 40 phr to about 90 phr, about 40 phr to about 80 phr, about29 phr to about 175 phr, about 40 phr to about 110 phr, about 50 phr toabout 175 phr, about 60 phr to about 175 phr, and the like. Thesilica-reinforced elastomer composite may optionally include a smallamount of carbon black for color, conductivity, and/or UV stabilityand/or for other purposes. Small amounts of carbon black contained inthe elastomer composite can range, for instance, from about 0.1 wt % toabout 10 wt %, based on the weight of the total particles present in theelastomer composite. Any grade or type of carbon black(s) can be used,such as reinforcing, or semi-reinforcing tire-grade furnace carbonblacks and the like. As an example, if carbon black or other filler isto be added and form part of the elastomer composite, the carbon blackor other filler can be added, for instance, using a 3-way mixing block.One example is shown in FIG. 1C. Using such a set-up, the carbon blackor other filler can be added simultaneously with the silica slurry inorder to provide a blend of reinforcing particles in the elastomercomposite. The carbon black can be dispersed in an aqueous slurry priorto use.

In any method of producing an elastomer composite, the method canfurther include one or more of the following steps, after formation ofthe solid or semi-solid silica-containing continuous rubber phase:

-   -   one or more holding steps or further solidification or        coagulation steps to develop further elasticity;    -   one or more dewatering steps can be used to de-water the        composite to obtain a dewatered composite;    -   one or more extruding steps;    -   one or more calendaring steps;    -   one or more milling steps to obtain a milled composite;    -   one or more granulating steps;    -   one or more baling steps to obtain a bailed product or mixture;    -   the baled mixture or product can be broken apart to form a        granulated mixture;    -   one or more mixing or compounding steps to obtain a compounded        composite.

As a further example, the following sequence of steps can occur and eachstep can be repeated any number of times (with the same or differentsettings), after formation of the solid or semi-solid silica-containingcontinuous rubber phase:

-   -   one or more holding steps or further coagulation steps to        develop further elasticity    -   dewatering the composite (e.g., the elastomer composite exiting        the reaction zone) to obtain a dewatered composite;    -   mixing or compounding the dewatered composite to obtain a        compounded mixture;    -   milling the compounded mixture to obtain a milled mixture (e.g.,        roll milling);    -   granulating or mixing the milled mixture;    -   optionally baling the mixture after the granulating or mixing to        obtain a baled mixture;    -   optionally breaking apart the baled mixture and mixing.

In any embodiment, a coupling agent can be introduced in any of thesteps (or in multiple steps or locations) as long as the coupling agenthas an opportunity to become dispersed in the elastomer composite. As anexample, one or more coupling agents (e.g., silane coupling agents) canbe reacted with the silica slurry (e.g., precipitated silica slurry)before the slurry is fed to the wet masterbatch reaction zone. Forinstance, the process described in U.S. Pat. No. 8,357,733 (incorporatedin its entirety by reference herein) can be implemented in the methodsof the present invention. Another example is to add one or more couplingagents (e.g., silane coupling agents) to the solid or semi-solidsilica-containing continuous rubber phase after coagulation, forinstance, prior to and/or during any downstream dewatering ormastication step with the preference of having sufficient heat presentto enhance reaction of silica with the coupling agent. Another examplecan be adding one or more coupling agents by way of a third inlet in areaction zone such as shown in FIG. 1C. This option can be optimized bypH adjustment such that the pH of the silica slurry is sufficiently highfor the coupling agent to react rapidly with the silica (e.g., a saltdestabilized silica) while being mixed with elastomer latex.

As just one example, the solid or semi-solid silica-containingcontinuous rubber phase exiting the reaction zone or area can betransferred by a suitable apparatus (e.g., belt or conveyor), to adewatering extruder. Suitable dewatering extruders are well known andcommercially available from, for example, the French Oil Mill MachineryCo. (Piqua, Ohio, USA). Alternatively or in addition, the solid orsemi-solid silica-containing continuous rubber phase may be compressed,for example, between metallic plates, to expel at least a portion of theaqueous fluid phase, e.g., to expel aqueous fluid until the watercontent of such material is below 40 wt %.

In general, the post processing steps can comprise compressing theelastomer composite to remove from about 1 wt % to about 15 wt % ormore, of an aqueous fluid phase, based on the total weight of theelastomer composite. The dewatering extruder may bring the silicaelastomer composite from, e.g., approximately about 40% to about 95%water content to approximately about 5% to about 60% water content (forexample, from about 5% to about 10% water content, from about 10% toabout 20% water content, from about 15% to about 30% water content, orfrom about 30% to about 50% water content) with all weight percent basedon total weight of composite. The dewatering extruder can be used toreduce the water content of the silica elastomer composite to about 35wt % or other amounts. The optimal water content may vary with theelastomer employed, the amount, and/or type of filler, and the devicesemployed for mastication of the dewatered product. The elastomercomposite may be dewatered to a desired water content, following whichthe resulting dewatered product can be further masticated while beingdried to a desired moisture level (e.g., from about 0.5% to about 10%,for example, from about 0.5% to about 1%, from about 1% to about 3%,about 3% to about 5%, or from about 5% to about 10%, preferably below 1%all weight percent based on total weight of product). The mechanicalenergy imparted to the material can provide improvement in rubberproperties. For example, the dewatered product may be mechanicallyworked with one or more of a continuous mixer, an internal mixer, a twinscrew extruder, a single screw extruder, or a roll mill. This optionalmixing step can have the ability to masticate the mixture and/orgenerate surface area or expose surface which can permit removal ofwater (at least a portion thereof) that may be present in the mixture.Suitable masticating devices are well known and commercially available,including for example, a Unimix Continuous Mixer and MVX (Mixing,Venting, eXtruding) Machine from Farrel Corporation of Ansonia, Conn.,USA, a long continuous mixer from Pomini, Inc., a Pomini ContinuousMixer, twin rotor co-rotating intermeshing extruders, twin rotorcounter-rotating non-intermeshing extruders, Banbury mixers, Brabendermixers, intermeshing-type internal mixers, kneading-type internalmixers, continuous compounding extruders, the biaxial milling extruderproduced by Kobe Steel, Ltd., and a Kobe Continuous Mixer. Alternativemasticating apparatus will be familiar to those of skill in the art andcan be used.

As dewatered product is processed in a desired apparatus, the apparatusimparts energy to the material. Without being bound by any particulartheory, it is believed that friction generated during mechanicalmastication heats the dewatered product. Some of this heat is dissipatedby heating and vaporizing the moisture in the dewatered product. Aportion of the water may also be removed by squeezing the material inparallel with heating. The temperature should be sufficiently high torapidly vaporize water to steam that is released to the atmosphereand/or is removed from the apparatus, but not so high as to scorch therubber. The dewatered product can achieve a temperature from about 130°C. to about 180° C., such as from about 140° C. to about 160° C.,especially when the coupling agent is added prior to or duringmastication. The coupling agent can include a small amount of sulfur,and the temperature should be maintained at a sufficiently low level toprevent the rubber from cross-linking during mastication.

As an option, additives can be combined with the dewatered product in amechanical mixer. Specifically, additives such as filler (which may bethe same as, or different from, the filler used in the mixer; exemplaryfillers include silica, carbon black, and/or zinc oxide), otherelastomers, other or additional masterbatch, antioxidants, couplingagents, plasticizers, processing aids (e.g., stearic acid, which canalso be used as a curing agent, liquid polymers, oils, waxes, and thelike), resins, flame-retardants, extender oils, and/or lubricants, and amixture of any of them, can be added in a mechanical mixer. Additionalelastomers can be combined with the dewatered product to produceelastomer blends. Suitable elastomers include any of the elastomersemployed in latex form in the mixing process described above andelastomers such as EPDM that are not available in latex form and may bethe same or different than the elastomer in the silica-containingelastomer composite. Exemplary elastomers include, but are not limitedto, rubbers, polymers (e.g., homopolymers, copolymers and/orterpolymers) of 1,3-butadiene, styrene, isoprene, isobutylene,2,3-dialkyl-1,3-butadiene, where alkyl may be methyl, ethyl, propyl,etc., acrylonitrile, ethylene, propylene, and the like. Methods ofproducing masterbatch blends are disclosed in commonly owned U.S. Pat.Nos. 7,105,595, 6,365,663, and 6,075,084 and PCT PublicationWO2014/189826. The antioxidant (an example of a degradation inhibitor)can be an amine type antioxidant, phenol type antioxidant, imidazoletype antioxidant, metal salt of carbamate, para-phenylene diamine(s)and/or dihydrotrimethylquinoline(s), polymerized quinine antioxidant,and/or wax and/or other antioxidants used in elastomer formulations.Specific examples include, but are not limited to,N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6-PPD, e.g.,ANTIGENE 6C, available from Sumitomo Chemical Co., Ltd. and NOCLAC 6C,available from Ouchi Shinko Chemical Industrial Co., Ltd.), “Ozonon” 6Cfrom Seiko Chemical Co., Ltd., polymerized 1,2-dihydro-2,2,4-trimethylquinoline (TMQ, e.g., Agerite Resin D, available from R. T. Vanderbilt),2,6-di-t-butyl-4-methylphenol (available as Vanox PC from VanderbiltChemicals LLC), butylhydroxytoluene (BHT), and butylhydroxyanisole(BHA), and the like. Other representative antioxidants may be, forexample, diphenyl-p-phenylenediamine and others such as, for example,those disclosed in The Vanderbilt Rubber Handbook (1978), pages 344-346.

Another improvement with the present invention is the option of making arubber compound that involves utilizing the method of the presentinvention by producing a silica elastomer composite as detailed herein.Then, the silica elastomer composite can be blended with othercomponents as indicated herein to form a rubber compound. The “othercomponents” can comprise at least one antioxidant and preferably thisantioxidant has a lower affinity to silica than the antioxidantN-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (“6-PPD”). An exampleof such an antioxidant is polymerized 2,2,4-trimethyl 1-1,2dihydroquinoline. A general class of such antioxidants are the quinloinetypes or the monophenol types. Commercial examples include AgeritieResin D pellets by Vanderbilt or Vanox PC by Vanderbilt. With such anoption, namely, the antioxidant(s) having a lower affinity for silica,this can avoid the quick adsorption of the antioxidant onto the silicasurface, leaving sufficient antioxidant available to protect thesurrounding rubber from oxidation. Also, by having less antioxidantbeing adsorbed onto the silica surface, the silica has greaterreactivity with any coupling agents present, resulting in bettercoupling of silica to rubber. Therefore, with this type of antioxidantin the process of the present invention, silica silanization and/orbound rubber formation can be enhanced or their inhibition can bereduced or avoided.

In general, if an antioxidant is added in making the rubber compound,the order of addition of the antioxidant(s) with any “other components”is not critical. More than one type of antioxidant can be use and/or oneor more antioxidants can be added at one or more stages of the processto make the rubber compound, including any one or more stages prior torubber formation and/or any of the stages or steps shown in FIG. 2.

The coupling agent can be or include one or more silane coupling agents,one or more zirconate coupling agents, one or more titanate couplingagents, one or more nitro coupling agents, or any combination thereof.The coupling agent can be or includebis(3-triethoxysilylpropyl)tetrasulfane (e.g., Si 69 from EvonikIndustries, Struktol SCA98 from Struktol Company),bis(3-triethoxysilylpropyl)disulfane (e.g., Si 75 and Si 266 from EvonikIndustries, Struktol SCA985 from Struktol Company),3-thiocyanatopropyl-triethoxy silane (e.g., Si 264 from EvonikIndustries), gamma-mercaptopropyl-trimethoxy silane (e.g., VP Si 163from Evonik Industries, Struktol SCA989 from Struktol Company),gamma-mercaptopropyl-triethoxy silane (e.g., VP Si 263 from EvonikIndustries), zirconium dineoalkanolatodi(3-mercapto) propionato-O,N,N′-bis(2-methyl-2-nitropropyl)-1,6-diaminohexane,S-(3-(triethoxysilyl)propyl) octanethioate (e.g., NXT coupling agentfrom Momentive, Friendly, W. Va.), and/or coupling agents that arechemically similar or that have the one or more of the same chemicalgroups. Additional specific examples of coupling agents, by commercialnames, include, but are not limited to, VP Si 363 from EvonikIndustries. It is to be appreciated that any combination of elastomers,additives, and additional masterbatch may be added to the dewateredproduct, for instance in a compounder.

As an option, the dewatered product can be masticated using an internalmixer such as a Banbury or Brabender mixer. The dewatered product mayfirst be brought to a moisture content of about 3 wt % to about 40 wt %,for example, about 5 wt % to about 20 wt %, or about 20 wt % to about 30wt %. The moisture content may be achieved by dewatering to the desiredlevel or by dewatering the dewatered product crumb to an intermediatemoisture content as the first step and then further reducing moisturecontent by heating the resulting dewatered product, or by letting waterevaporate from the dewatered product at room temperature, or by othermethods familiar to those of skill in the art. The dewatered product maythen be masticated in an internal mixer until a desired moisture levelor mechanical energy input is achieved. The dewatered product can bemasticated until it reaches a predetermined temperature, allowed tocool, and then placed back into the internal mixer one or more times toimpart additional energy to the material. Examples of temperaturesinclude from about 140° C. to about 180° C., for example, from about145° C. to about 160° C., or from about 150° C. to about 155° C. Thedewatered product may be sheeted in a roll mill after each masticationin the internal mixer. Alternatively or in addition, dewatered productthat has been masticated in a Banbury or Brabender mixer may be furthermasticated in an open mill.

As an option, the masticated product can be further processed on an openmill. The masticated product can be discharged from the continuouscompounder as a length of extrudate and may be cut into smaller lengthsprior to entering the open mill. The masticated product may optionallybe fed to the open mill via a conveyor. The conveyor may be a conveyorbelt, conduit, pipe, or other suitable means for transporting themasticated product from a continuous compounder to an open mill. Theopen mill can include a pair of rollers that may optionally be heated orcooled to provide enhanced operation of the open mill. Other operatingparameters of the open mill can include the gap distance between therolls, the bank height, i.e., the reservoir of material in the gapbetween and on top of the rolls, and the speed of each roll. The speedof each roll and the temperature of the fluid used to cool each roll maybe controlled independently for each roll. The gap distance may be fromabout 3 mm to about 10 mm or from about 6 mm to about 8 mm. The rollspeed may be about 15 rpm to about 70 rpm, and the rollers may rolltowards one another with respect to the inlet side of the mill. Thefriction ratio, the ratio of the speed of the collection roller, e.g.,the roller on which the masticated product collects, to that of the backroller, may be from about 0.9 to about 1.1. The fluid employed to coolthe rollers may be from about 35° C. to about 90° C., for example, fromabout 45° C. to about 60° C., from about 55° C. to about 75° C., or fromabout 70° C. to about 80° C. In addition to controlling the operation ofthe open mill to provide a desired level of mastication and desiccationto the masticated product, it is also desirable that the output of theopen mill should collect on the collection roller as a smooth sheet.Without being bound by any particular theory, it is thought that coolerroller temperatures facilitate this goal. The open mill may reduce thetemperature of the masticated product to approximately about 110° C. toabout 140° C. The residence time of the masticated product in the millcan be determined in part by the roller speed, the gap distance and theamount of mastication and drying desired and may be about 10 minutes toabout 20 minutes for material that has already been masticated, forexample, in a twin-rotor continuous mixer.

One skilled in the art will recognize that different combinations ofdevices may be employed to provide mastication and desiccation to asolid silica-containing continuous rubber phase produced according tothe various embodiments. Depending on which devices are used, it may bedesirable to operate them under different conditions than thosedescribed above to impart varying amounts of work and desiccation to thematerial. In addition, it may be desirable to employ more than oneparticular kind of device, e.g., an open mill or internal mixer, inseries or to pass masticated product through a given device more thanone time. For example, the masticated product may be passed through anopen mill two or three or more times or passed through two or three ormore open mills in series. In the latter case, it may be desirable tooperate each open mill under different operating conditions, e.g.,speed, temperature, different (e.g. higher) energy input, etc.Masticated product can be passed through one, two, or three open millsafter being masticated in an internal mixer.

The elastomer composite may be used to produce an elastomer or rubbercontaining product. As an option, the elastomer composite may be used inor produced for use in various parts of a tire, for example, tires, tiretreads, tire sidewalls, wire-skim for tires, and cushion gum for retreadtires. Alternatively or in addition, elastomer composite may be used forhoses, seals, gaskets, anti-vibration articles, tracks, track pads fortrack-propelled equipment such as bulldozers, etc., engine mounts,earthquake stabilizers, mining equipment such as screens, miningequipment linings, conveyor belts, chute liners, slurry pump liners, mudpump components such as impellers, valve seats, valve bodies, pistonhubs, piston rods, plungers, impellers for various applications such asmixing slurries and slurry pump impellers, grinding mill liners,cyclones and hydrocyclones, expansion joints, marine equipment such aslinings for pumps (e.g., dredge pumps and outboard motor pumps), hoses(e.g., dredging hoses and outboard motor hoses), and other marineequipment, shaft seals for marine, oil, aerospace, and otherapplications, propeller shafts, linings for piping to convey, e.g., oilsands and/or tar sands, and other applications where abrasion resistanceand/or enhanced dynamic properties are desired. The vulcanized elastomercomposite may be used in rollers, cams, shafts, pipes, tread bushingsfor vehicles, or other applications where abrasion resistance and/orenhanced dynamic properties are desired.

Traditional compounding techniques may be used to combine vulcanizationagents and other additives known in the art, including the additivesdiscussed above in connection with the dewatered product, with the driedelastomer composite, depending on the desired use.

The present invention further relates to an elastomer composite formedby any one or more methods described herein of the present invention.

Unless otherwise specified, all material proportions described as apercent herein are in weight percent.

The present invention will be further clarified by the followingexamples which are intended to be only exemplary in nature.

Silica Examples Silica Example 1

The following materials are placed into a stainless steel reactorequipped with a propeller-type agitating system and a double-jacketedheater: (i) 660 liters of water, (ii) 11.8 kg of Na2SO4 (electrolyte),(iii) 323 liters of aqueous sodium silicate having an SiO2/Na2O weightratio of 3.45:1 and a density at 20° C. of 1,230.

The concentration of SiO2 in the sediment (or vessel bottoms) is then 77g/l. The mixture is heated to a temperature of 82° C. and agitation ismaintained. 395 liters of dilute aqueous sulfuric acid having a densityat 20° C. of 1.050 are added until a pH value of 7.5 is attained in thereaction medium (measured at the temperature thereof). The reactiontemperature is 82° C. during the first 15 minutes of reaction; it isthen adjusted from 82° to 95° C. over 15 minutes, and maintained at 95°C. until the reaction is completed.

A total of 77 liters of aqueous sodium silicate of the type describedabove and 106 liters of sulfuric acid, also of the type described above,are then together added to the reaction medium. The simultaneousaddition of acid and silicate is carried out in such manner that the pHof the reaction medium during their addition is constantly maintained at7.5+/−0.1. When all of the silicate had been introduced, introduction ofthe dilute acid is continued for 5 minutes at a flow rate of 310 l/h.The introduction of the additional acid adjusted the pH of the medium toa value of 5.0. After a total reaction time is fixed at 85 minutes, apulp of precipitated silica is obtained. It is filtered and washed bymeans of a filter press, such that a silica cake is ultimatelyrecovered, exhibiting an ignition weight loss of 79% (hence, theproportion of dry solids is 21% by weight). The filter cake is fluidizedby mechanical action. After this disintegrating operation, a pumpablecake is produced having a pH of 6.3.

Silica Example 2

A total of 10 liters of purified water is introduced into a 25-literstainless steel reactor. The solution is brought to 80° C. The entirereaction is carried out at this temperature. With stirring (350 rpm,propeller-type stirring), 80 g/l sulfuric acid is introduced until thepH reaches a value of 4.

There are introduced simultaneously into the reactor over 35 minutes asolution of sodium silicate (of weight ratio SiO2/Na2O equal to 3.52)having a concentration of 230 g/l and at a flow rate of 76 g/min andsulfuric acid of a concentration equal to 80 g/l at a flow rateregulated so as to keep the pH of the reaction medium at a value of 4.After 30 minutes, the stirring rate is brought to 450 rpm.

At the end of 35 minutes of simultaneous addition, the introduction ofacid is stopped as long as the pH has not reached a value equal to 9.The flow of silicate is then stopped. A maturation of 15 minutes at pH 9follows. At the end of the maturation, the stirring rate is brought to350 rpm. The pH is then brought to pH 8 by introduction of sulfuricacid. Another simultaneous addition is effected for 40 minutes with aflow rate of sodium silicate of 76 g/min (same sodium silicate as forthe first simultaneous addition) and a flow rate of sulfuric acid of aconcentration equal to 80 g/l regulated so as to keep the pH of thereaction medium at a value of 8.

After this simultaneous addition, the reaction medium is brought to a pHof 4 by adding 80 g/l sulfuric acid. The medium is matured for 10minutes at pH 4. A flocculant FA 10 (polyoxyethylene of a molar massequal to 5×10⁶ g; BASF-Wyandotte Corporation) 250 ml at 1% is introducedat the 3rd minute of the maturation. The slurry is filtered and washedin a vacuum (dry extract of 16.7%). After dilution (dry extract of 13%),the filter cake obtained is disintegrated mechanically.

Silica Example 3

In sample 3-1, a total of 43.5 m³ of hot water is introduced into a vatand commercial sodium water glass (weight modulus 3.42, density 1.348)is stirred in a quantity to yield a pH of 8.5. While maintaining aprecipitation temperature of 88° C. and pH 8.5, 16, 8 m³ of the samewater glass and sulfuric acid (96%) are simultaneously added over 150minutes from inlets at opposite sides of the vat. A solids content of100 g/l is produced. Further sulfuric acid is then added until a pH of<5 is achieved. The solids are separated in presses and washed.

The same procedure is repeated for sample 3-2, with the exception that apH value of 9.0 is maintained in the initial precipitation batch andduring precipitation. After 135 minutes, a solids content of 98 g/l isachieved in the precipitation suspension.

The same procedure used for sample 3-2 is repeated for sample 3-3, withthe difference that the precipitation time is shortened to 76 minutesand the precipitation temperature reduced to 80° C. After this period, asolids content in the precipitation suspension of 100 g/l is achieved.

Silica Example 4

To prepare a slurry of silica pre-treated with a coupling agent, anaqueous solution of silane is prepared by charging to a vessel 4 gramsof isopropanol, 2.36 grams of bis-(3-trimethoxysilylpropyl) disulfide(TMSPD), which is prepared using the procedure of U.S. Pat. No.5,440,064 and which contains essentially no condensation products (6.0%by weight of the silica to be charged later), and 0.7 grams of aceticacid. The mixture is then stirred vigorously at room temperature while96 grams of water is slowly added. The mixture is then stirred for afurther 15 minutes until the solution clears.

In a separate vessel equipped with a stirrer, 196 grams of silica cakemade according to Silica Example 1 (20% solids with the remainder beingwater) and 331 grams of water are charged. The mixture is then stirredfor 15 minutes to ensure the cake is completely dispersed. Then theaqueous silane solution is added and stirred for a further 30 minutes.Using a 25% NaOH solution, the pH of the mixture is increased to 7.5.The mixture is then heated to approximately 70° C. for 4 hours whilecontinuously mixing. The product is filtered and a silanized silicamaterial containing about 20% by wt solids, and about 80% aqueousmedium, is recovered.

Silica Example 5

To prepare a silica sol containing approximately 2 wt % of silica, ionexchange resin (Lewatit Monoplus 108; Lanxess Deutschland GmbH,Leverkusen, Germany) is activated in a column by eluting it with H₂SO₄until the pH of the eluent is below 2. Then it is neutralized by passingdeionized water through the resin until the ion conductivity of theeluent is 5 pS/cm.

In a 2 L vessel equipped with stirrer and cooling unit, 1 L of wet ionexchange resin and 225 g of deionized water are cooled to 6° C. andstirred vigorously. Then 550 g of a sodium water glass solution with4.875 wt % SiO₂ are prepared by diluting a commercial sodium water glasssolution (37/38 alkali silicate from Woellner GmbH, Ludwigshafen,Germany) with deionized water. This solution is added to the vessel viaa peristaltic pump with an addition rate of 23 ml/min. Temperature ismaintained below 12° C. When sodium water glass addition is completed,the mixture is stirred for 15 min at below 12° C. The liquid phase isdecanted from the resin and passed via a Buchner funnel through a filter(Whatmann, 0.7 μm). The sol is collected in a 5 L washing bottle andcharacterized. A total of 744.5 g of silica sol with a solid content of2.21 wt % (density@20° C.=1.0116 kg/L, pH=3.2) is obtained. The SiO₂content is adjusted to 1.94 wt % with deionized water and the resultingsol used immediately to coat carbon black.

For the coating step, 25.0 g of fluffy carbon black (N115 ASTM grade; I₂No=147 mg/g; Cabot Corporation, Boston, Mass.) are dispersed in 1250 gof deionized water by shear mixing at 25,000 rpm for 5 min to yield adispersion containing 2 wt % of carbon black. The resulting dispersionis transferred to a jacketed glass vessel (2 L) equipped with athermostat and a stirrer. Temperature and pH are monitored. Stirring isstarted and the slurry is heated to 80° C.

To yield a final SiO₂/CB ratio of 0.35 in the batch, 451.9 g of thesilica sol (1.94% SiO₂, density@20° C.=1.0099 kg/L) are added via aperistaltic pump with an addition rate of 15 g/min. The pH is controlledand the dispersion is stirred for 5 min at 80° C. Then the coated carbonblack is separated from the liquid phase by vacuum filtration. Thefiltrate is characterized by a pH=4.1, density@20° C.: 998.6 kg/L; 0.1wt % SiO₂, and conductivity: 48.5 S/cm.

To remove any residual silica, the solid product is redispersed indeionized water (80° C.) and filtered until the conductivity of thewashing water is close to deionized water. A total of 168.8 g of a solidfilter cake is obtained, consisting of 19.7% SiO2 and carbon black andabout 80% of water. (Silica content is determined by ashing the coatedcarbon black in a muffle furnace for 5 h at 600° C.) The SiO₂/CB ratioin the product is determined to be 0.35 and the product contained 25 wt% silica on a total product weight basis.

The wet filter cakes obtained from Silica Examples 1-5 are adjusted withwater to a solids level of 10-25% silica, and re-slurried with amechanical agitator. Optionally, the resulting silica slurry is milledso as to fluidize the slurry, reduce silica particle agglomeration,control silica particle size distribution, and/or reduce the viscosityof the silica slurry. At this point the silica material can be pumped asa liquid slurry. Any grinding or further mechanical processing of thesilica slurry can be carried out by adapting the techniques describedbelow in the Masterbatch Examples to the never-dried silica slurriesmade according to Silica Examples 1-5, above. Likewise never-driedsilica slurries made according to Silica Examples 1-5 may be adjusted totarget solids contents, ionic concentration, pH, and degree ofdestabilization by techniques described below in the MasterbatchExamples. The re-slurried precipitated silica is pumped to the reactionzone of a continuous reactor, such as described herein and in theFigures. The processes described in the Masterbatch Examples below(e.g., Example 4) are used to form the silica elastomer compositecomprising never-dried silica particles. Because the silica particleshave been engulfed by rubber molecules in the latex before drying,particle compaction and silica-silica bonding may be greatly reduced orrendered insignificant relative to wet masterbatch processes using drysilica production materials. Processes described herein utilizingnever-dried silica yield silica elastomer composites with excellentlevels of silica dispersion, both at the macro- and micro-dispersionlevels. The excellent silica dispersion leads to improved wear, abrasionand other mechanical properties after compounding and vulcanization ofthe silica elastomer composite.

Masterbatch Examples

In these examples, the “field latex” was field latex (Muhibbah LateksSdn Bhd, Malaysia) having a dry rubber content of about 30 wt %. The“latex concentrate” was latex concentrate (high ammonia grade, fromMuhibbah Lateks Sdn Bhd, Malaysia, or from Chemionics Corporation,Tallmadge, Ohio) diluted by about 50% to a dry rubber content of about30 wt % using either pure water or water with 0.6 wt % to 0.7 wt %ammonia. Unless noted otherwise below in these Masterbatch Examples, the“silica” was ZEOSIL® Z1165 MP precipitated silica from Solvay USA Inc.,Cranbury, N.J. (formerly Rhodia). However, for each Masterbatch Examplebelow, a never-dried silica slurry prepared by a method of SilicaExamples 1-5 as described above may be adjusted to the parameters of,and substituted for, the first fluid of such Masterbatch Example with anequivalent effect.

Thermogravimetric Analysis.

The actual silica loading levels were determined by thermogravimetricanalysis (TGA) following the ISO 6231 method.

Water Content of Product.

The test material was cut into mm size pieces and loaded into themoisture balance (e.g., Model MB35 and Model MB45; Ohaus Corporation,Parsippany N.J.) for measurement. The water content was measured at 130°C. for 20 minutes to 30 minutes until the test sample achieved aconsistent weight.

Slurry Zeta Potential.

In these examples, the zeta potential of particulate slurries wasmeasured using a ZetaProbe Analyzer™ from Colloidal Dynamics, LLC, PonteVedra Beach, Fla. USA. With multi-frequency electroacoustic technology,the ZetaProbe measures zeta potential directly at particleconcentrations as high as 60% by volume. The instrument was firstcalibrated using the KSiW calibration fluid provided by ColloidalDynamics (2.5 mS/cm). A 40 g sample was then placed into a 30 mL Tefloncup (Part #A80031) with a stir bar, and the cup was placed on a stirringbase (Part #A80051) with 250 rpm stirring speed. The measurement wasperformed using the dip probe 173 in a single-point mode with 5-pointrun at ambient temperature (approximately 25° C.). The data wereanalyzed using ZP version 2.14c Polar™ software provided by ColloidalDynamics. The zeta potential values can be negative or positivedepending on polarity of charge on the particles. The “magnitude” ofzeta potential refers to the absolute value (e.g., a zeta potentialvalue of −35 mV has a higher magnitude than a zeta potential value of−20 mV). The magnitude of the zeta potential reflects the degree ofelectrostatic repulsion between similarly charged particles indispersion. The higher the magnitude of zeta potential, the more stableof particles in dispersion. Zeta potential measurements were carried outon particulate silica slurries prepared as described below.

Dry silica was weighed and combined with deionized water using a5-gallon bucket and a high shear overhead laboratory mixer with ashrouded agitator (Silverson Model AX3, Silverson Machines, Inc., EastLongmeadow, Mass.; operating at 5200-5400 rpm for 30 minutes to 45minutes). Once the silica was roughly dispersed in water and able to bepumped, the silica slurry was transferred via a peristaltic pump(Masterflex 7592-20 system—drive and controller, 77601-10 pump headusing I/P 73 tubing; Cole-Palmer, Vernon Hills, Ill.) into a mixing loopwith an inline high shear rotor-stator mixer (Silverson Model 150LBlocated after the peristaltic pump, operated at 60 Hz) in a run tank (30gal. convex bottom port vessel) and was ground to further break downsilica agglomerates and any remaining silica granules. The slurry in therun tank was then circulated at 2 L/min using the same peristaltic pumpthrough the mixing loop for a time sufficient for turnover of at least5-7 times of the total slurry volume (>45 minutes) to make sure anysilica agglomerates were properly ground and distributed. An overheadmixer (Ika Eurostar power control visc-P7; IKA-Works, Inc., Wilmington,N.C.) with a low shear anchor blade rotating at about 60 rpm was used inthe run tank to prevent gelling or sedimentation of silica particles. Anacid (formic acid or acetic acid, reagent grade from Sigma Aldrich, St.Louis, Mo.) or salt (calcium nitrate, calcium chloride, calcium acetateor aluminum sulfate, reagent grade from Sigma Aldrich, St. Louis, Mo.)was added to the slurry in the run tank after grinding. The amount ofsilica in the slurry and the type and concentration of acid or salt areindicated in the specific Examples below.

Exemplary Process A.

Where indicated in the examples below, a method was carried oututilizing Exemplary Process A. In Process A, dry precipitated silica andwater (municipal water filtered to remove particulate matter) weremetered and combined and then ground in a rotor-stator mill to formsilica slurry, and the silica slurry was further ground in a feed tankusing an agitator and another rotor-stator mill. The silica slurry wasthen transferred to a run tank equipped with two stirrers. The silicaslurry was recirculated from the run tank through a homogenizer and backinto the run tank. A solution of acid (formic acid or acetic acid,industrial grade obtained from Kong Long Huat Chemicals, Malaysia) orsalt (calcium nitrate, industrial grade obtained from Mey ChernChemicals, Malaysia) was then pumped into the run tank. The slurry wasmaintained in dispersed form through stirring and, optionally, by meansof the recirculating loop in the run tank. After a suitable period, thesilica slurry was fed to a confined reaction zone (13), such as the oneshown in FIG. 1A, by means of the homogenizer. The concentration ofsilica in the slurry and the concentration of acid or calcium nitrateare indicated in the specific Examples below.

The latex was pumped with a peristaltic pump (at less than about 40 psigpressure) through the second inlet (11) into the reaction zone (13). Thelatex flow rate was adjusted between about 300-1600 kg latex/hr in orderto obtain a desired production rate and silica loading levels in theresulting product. The homogenized slurry containing acid, or salt, or acombination of acid and salt, was pumped under pressure from thehomogenizer to a nozzle (0.060″-0.130″ inside diameter (ID)) (3 a),represented by the first inlet (3) shown in FIG. 1A, such that theslurry was introduced as a high speed jet into the reaction zone. Uponcontact with the latex in the reaction zone, the jet of silica slurryflowing at a velocity of 25 m/s to 120 m/s entrained the latex flowingat 1 m/s to 11 m/s. In Examples according to embodiments of theinvention, the impact of the silica slurry on the latex caused anintimate mixing of silica particles with the rubber particles of thelatex, and the rubber was coagulated, transforming the silica slurry andthe latex into a material comprising a solid or semi-solidsilica-containing continuous rubber phase containing 40 to 95 wt %water, based on total weight of the material, trapped within thematerial. Adjustments were made to the silica slurry flow rate (500-1800kg/hr), or the latex flow rate (300-1800 kg/hr), or both, to modify thesilica to rubber ratios (e.g., 15-180 phr silica) in the final product,and to achieve the desired production rate. The production rates (drymaterial basis) were 200-800 kg/hr. Specific silica contents (by TGAanalysis) in the rubber following dewatering and drying of the materialare listed in the Examples below.

Process A Dewatering.

Material was discharged from the reaction zone at atmospheric pressureat a flow rate from 200 to 800 kg/hr (dry weight) into a dewateringextruder (The French Oil Machinery Company, Piqua, Ohio). The extruder(8.5 inch I.D.) was equipped with a die plate with various die-holebuttons configurations and operated at a typical rotor speed of 90 to123 RPM, die plate pressure 400-1300 psig, and power of 80 kW to 125 kW.In the extruder, silica-containing rubber was compressed, and the watersqueezed out of the silica-containing rubber was ejected through aslotted barrel of the extruder. Dewatered product typically containing15-60 wt % water was obtained at the outlet of the extruder.

Process A Drying and Cooling.

The dewatered product was dropped into a continuous compounder (FarrelContinuous Mixer (FCM), Farrel Corporation, Ansonia, Conn.; with #7 and15 rotors) where it was dried, masticated and mixed with 1-2 phr ofantioxidant (e.g. 6PPD from Flexsys, St. Louis, Mo.) and optionallysilane coupling agent (e.g. NXT silane, obtained from MomentivePerformance Materials, Inc., Waterford, N.Y.; 8 wt % silane on silicaweight basis). The temperature of the FCM water jacket was set at 100°C., and the FCM temperature at the output orifice was 140° C. to 180° C.The moisture content of the masticated, dewatered elastomer compositeexiting the FCM was around 1 wt % to 5 wt %. The product was furthermasticated and cooled on an open mill. A rubber sheet of the elastomercomposite was directly cut from the open mill, rolled and cooled in air.

Exemplary Process B.

Where indicated in the examples below, an exemplary method was carriedout utilizing Exemplary Process B. In Process B, dry silica was weighedand combined with deionized water using a 5-gallon bucket and a highshear overhead laboratory mixer with a shrouded agitator (SilversonModel AX3, Silverson Machines, Inc., East Longmeadow, Mass.; operatingat 5200 rpm to 5400 rpm for 30-45 minutes). Once the silica was roughlydispersed in water and able to be pumped, the silica slurry wastransferred via a peristaltic pump (Masterflex 7592-20 system—drive andcontroller, 77601-10 pump head using I/P 73 tubing; Cole-Palmer, VernonHills, Ill.) into a mixing loop with an inline high shear rotor-statormixer (Silverson Model 150LB located after the peristaltic pump,operated at 60 Hz) in a run tank (30 gal convex bottom port vessel) andwas ground to further break down silica agglomerates and any remaininggranules. The slurry in the run tank was then circulated at 2 L/minthrough the mixing loop for a time sufficient for turnover of at least5-7 times of the total slurry volume (>45 minutes) to make sure anysilica agglomerates were properly ground and dispersed. An overheadmixer (Ika Eurostar power control visc-P7; IKA-Works, Inc., Wilmington,N.C.) with a low shear anchor blade rotating at about 60 rpm was used inthe run tank to prevent gelling or sedimentation of silica particles. Anacid (formic acid or acetic acid, reagent grade from Sigma Aldrich, St.Louis, Mo.) or salt (calcium nitrate, calcium chloride, calcium acetate,or aluminum sulfate salt, reagent grade from Sigma Aldrich, St. Louis,Mo.) was added to the slurry in the run tank after grinding. The amountof silica in the slurry and the type and concentration of acid or saltare indicated in Table 4 for the specific Examples below.

The latex was pumped using a peristaltic pump (Masterflex 7592-20system—drive and controller, 77601-10 pump head using I/P 73 tubing;Cole-Palmer, Vernon Hills, Ill.) through a second inlet (11) and into areaction zone (13) configured similarly to that shown in FIG. 1B. Thelatex flow rate was adjusted between about 25 kg/h to about 250 kg/h inorder to modify silica to rubber ratios of the elastomer composites.

When the silica was well dispersed in the water, the slurry was pumpedfrom the run tank through a diaphragm metering pump (LEWA-NikkisoAmerica, Inc., Holliston, Mass.) through a pulsation dampener (to reducepressure oscillation due to the diaphragm action) into either thereaction zone or the run tank via a recycle loop “T” connector. Thedirection of the slurry was controlled by two air actuated ball valves,one directing the slurry to the reaction zone and the other directingthe slurry to the run tank. When ready to mix the silica slurry withlatex, the line feeding the first inlet (3) to the reaction zone waspressurized to 100 psig to 150 psig by closing both valves. The ballvalve directing the slurry to the reaction zone was then opened andpressurized silica slurry was fed to a nozzle (0.020′ to 0.070″ ID) (3a) shown in FIG. 1B, at an initial pressure of 100 psig to 150 psig,such that the slurry was introduced as a high speed jet into thereaction zone. Upon contact with the latex in the reaction zone, the jetof silica slurry flowing at a velocity of 15 m/s to 80 m/s entrained thelatex flowing at 0.4 m/s to 5 m/s. In Examples according to embodimentsof the invention, the impact of the silica slurry on the latex caused anintimate mixing of silica particles with the rubber particles of thelatex, and the rubber was coagulated, transforming the silica slurry andthe latex into an elastomer composite comprising the silica particlesand 40 wt % to 95 wt % water trapped within a solid or semi-solidsilica-containing, continuous rubber phase. Adjustments were made to thesilica slurry flow rate (40 kg/hr to 80 kg/hr) or the latex flow rate(25 kg latex/hr to 300 kg latex/hr), or both, to modify silica to rubberratios (e.g., 15 phr to 180 phr silica) in the resulting product and toachieve the desired continuous production rates (30 kg/hr to 200 kg/hron dry material basis). Specific silica to rubber ratio (phr) contentsfollowing dewatering and drying are listed in the Examples below.

Process B Dewatering.

Material discharged from the reaction zone was recovered and sandwichedbetween two aluminum plates inside a catch pan. The “sandwich” was theninserted between two platens of a hydraulic press. With 2500 psigpressure exerted on the aluminum plates, water trapped inside the rubberproduct was squeezed out. If needed, the squeezed material was foldedinto a smaller piece and the squeezing process was repeated using thehydraulic press until the water content of the rubber product was below40 wt %.

Process B Drying and Cooling.

The dewatered product was put into a Brabender mixer (300 cc) for dryingand mastication to form a masticated, dewatered elastomer composite.Sufficient dewatered material was charged into the mixer to cover therotors. The initial temperature of the mixer was set at 100° C. and therotor speed was generally at 60 rpm. The water remaining in thedewatered product was converted to steam and evaporated out of the mixerduring the mixing process. As the material in the mixer expanded asresult of evaporation, any overflowing material was removed asnecessary. Either or both of a silane coupling agent (NXT silane,obtained from Momentive Performance Materials, Inc., Waterford, N.Y.; 8wt % silane on silica weight basis) and/or antioxidant (6-PPD,N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine, Flexsys, St. Louis,Mo.) was optionally added to the mixer when the mixer temperature wasabove 140° C. When the temperature of the mixer reached 160° C., thematerial inside the mixer was held at 160° C. to 170° C. by varying therotor speed for 2 minutes before the material was dumped. Themasticated, dewatered elastomer composite was then processed on an openmill. The moisture content of the material being taken off of the milltypically was below 2 wt %.

Preparation of Rubber Compounds.

Dried elastomer composite obtained by either Process A or Process B wascompounded according to the formulation in Table A and the procedureoutlined in Table B. For silica elastomer composites where either silaneor antioxidant was added during drying, the final compound compositionis as specified in Table A. The amount of silane coupling agent and/orantioxidant added during compounding was adjusted accordingly.

TABLE A Ingredient phr NR in Composite 100 Silica in Composite S 6PPD*(antioxidant) 2.0 Silane (NXT silane**) 0.08 × (phr silica) ZnO 4Stearic acid 2 DPG*** 1.5 Cure Rite ® BBTS**** 1.5 Sulfur 1.5*N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (Flexsys, St. Louis,MO) **main active component: S-(3-(triethoxysilyl)propyl)octanethioate(Momentive, Friendly, WV) ***DiphenylGuanidine (Akrochem, Akron, OH)****N-tert-Butylbenzothiazole-2-sulphenamide (Emerald PerformanceMaterials, Cuyahoga Falls, OH) NR = natural rubber S = as stated

TABLE B Time (min) Operation Stage 1 Brabender mixer (300 cc), 65% fillfactor, 60 rpm, 100° C. 0 Add rubber-silica composite 1 Add silanecoupling agent, if needed Hold for 2 minutes beginning at 150° C. 2Sweep and add 6PPD and mix for 1 additional minute at 150° C. 3 SweepDump, 160° C. Pass through roll mill 6x Stage 2 Brabender mixer (300cc), 63% fill factor, 60 rpm, 100° C. 0 Add stage 1 compound 1 Add zincoxide and stearic acid 2 Sweep 4 Dump, 150° C. Pass through roll mill 6xStage 3 Brabender mixer (300 cc), 63% fill factor, 60 rpm, 100° C. 0 Addstage 2 compound, sulfur and accelerators 0.5 Sweep 1 Dump Roll mill forone minute with adequate band. Remove and perform 6 end rolls. Sheet offto required thickness.

Vulcanization was carried out in a heated press set at 150° C. for atime determined by a conventional rubber rheometer (i.e., T90+10% ofT90, where T90 is the time to achieve 90% vulcanization).

Properties of Rubber/Silica Compounds.

The tensile properties of vulcanized samples (T300 and T100, elongationat break, tensile strength) were measured according to ASTM standardD-412. Tan delta 600 was determined using a dynamic strain sweep intorsion between 0.01% and 60% at 10 Hz and 60° C. Tan δ_(max) was takenas the maximum value of tan δ 60 within this range of strains.

Example 1

A silica slurry with 27.8 wt % Zeosil® 1165 silica was prepared asdescribed above in connection with the Slurry Zeta Potential testmethod. The slurry was then diluted using either deionized water or asupernatant obtained from ultracentrifugation of the 27.8 wt % slurry tomake a series of silica slurries at various silica concentrations. Thezeta potential of various silica slurries was measured to show therelationship between the concentration of the silica in the slurry andthe zeta potential of the slurry. The zeta potential of the silicaslurry, as shown in Table 1, appears to depend upon the silicaconcentration when the silica slurry is made using deionized water.However, as shown in Table 2, when slurry was diluted using thesupernatant obtained from ultracentrifugation of the 27.8 wt % slurry,the zeta potential stays roughly the same at different silicaconcentrations.

TABLE 1 Zeta potential of slurry of silica made using deionized water.Silica Concentration in slurry (w/w) 6% 10% 15% 20% 22% 25% ZetaPotential (mV) −46.4 −42.7 −39.6 −36.2 −34.7 −32.3 pH 5.19 5.04 4.924.86 4.83 4.77

TABLE 2 Zeta potential of silica slurry made from dilution of a 27.8 wt% silica slurry using the supernatant of the 27.8 wt % silica slurry.Silica Concentration in slurry (w/w) 6% 22% Zeta Potential (mV) −31.5−31.4 pH 4.86 4.79

This result demonstrates that an increase of magnitude of zeta potentialwhen such silica slurries are diluted with deionized water is mostly dueto reduction of ionic strength of the slurry. The ions in the silicaslurry are believed to be from residual salts present in the silica fromthe silica particle manufacturing process. The high magnitude of zetapotential of the silica slurries (all over 30 mV) indicated that thesilica has high electrostatic stability in the slurry.

Example 2

The effect of adding salt or acid at various concentrations to silicaslurries on the zeta potential of these slurries is set forth in Table3. Slurries were prepared in deionized water by the Slurry ZetaPotential test method described above. Data summarized in Table 3illustrate the dependence of zeta potential of silica slurries anddestabilized silica slurries on the silica concentration, saltconcentration, and acid concentration. Adding salt or acid to silicaslurry reduces the magnitude of zeta potential, thus the stability ofthe silica slurry. As shown in Table 3, the zeta potential dependsmostly on the concentration of salt or acid in the slurry ordestabilized slurry, and not on silica concentration.

TABLE 3 Zeta potential of slurry and destabilized of silica at variousslurry concentrations, salt concentrations, and acid concentrations.[acetic [formic Silica Concentration [CaCl₂] acid] acid] Zeta in Slurry(wt %) (mM) (mM) (mM) (mV) pH 22.0 0 0 0 −34.4 4.80 6.0 0 0 0 −45.0 ND22.0 10.6 0 0 −24.2 4.49 22.0 29.7 0 0 −17.0 4.27 22.0 51.1 0 0 −14.64.17 22.0 105 0 0 −9.2 ND 22.0 155 0 0 −6.4 ND 6.0 4.6 0 0 −29.9 ND 6.010.4 0 0 −23.4 ND 6.0 27.6 0 0 −18.5 ND 6.0 46.4 0 0 −15.4 ND 6.0 140 00 −7.7 ND 22.0 0 98 0 −23.6 3.72 22.0 0 192 0 −21.4 3.65 22.0 0 564 0−17.1 3.26 22.0 0 1857 0 −12.7 ND 6.0 0 27 0 −33.6 3.84 6.0 0 45 0 −29.93.68 6.0 0 174 0 −22.1 3.38 6.0 0 431 0 −18.9 3.61 22.0 0 0 118 −15.33.17 22.0 0 0 197 −14.2 2.96 22.0 0 0 731 −10.7 2.46 22.0 0 0 1963 −6.52.04 6.0 0 0 36 −17.7 3.07 6.0 0 0 42 −17.4 3.04 6.0 0 0 168 −14.6 2.626.0 0 0 456 −11.4 2.29 22.0 10.7 0 130 −12.9 3.04 22.0 26.6 0 248 −9.02.78 22.0 101 0 978 −3.1 2.10 6.0 4.7 0 36 −15.9 3.12 6.0 46.4 0 224−10.1 2.41 ND = not determined.

Results shown in Table 3 illustrate the dependence of zeta potential ofsilica slurries and destabilized silica slurries on acetic acidconcentration and silica concentration. The data show that the zetapotential values are more dependent on the acid concentration than thesilica concentration. A similar relationship between zeta potential toacid concentration and silica concentration is observed for formic acid.At a given concentration, formic acid reduces zeta potential magnitudemore than acetic acid. As shown in Table 3, a combination of formic acidand calcium chloride was effective in reducing the zeta potentialmagnitude. The results in Table 3 show that the stability of silicaparticles in slurry can be reduced effectively through addition ofdestabilization agents, such as acid or salt or a combination of acidand salt. Similar results were seen for calcium nitrate and calciumacetate.

Example 3

In this example, the importance of destabilizing the dispersion ofsilica particles prior to contacting the silica dispersion withelastomer latex was established. Specifically, four experiments were runusing the mixing apparatus of FIG. 1C, equipped with three inlets (3,11, 14) for introducing up to three fluids into a confined reaction zone(13), such that one fluid impacted the other fluids at a 90 degree angleas a high speed jet at a velocity of 15 m/s to 80 m/s (See FIG. 1C). Inthree of the four experiments, the silica was ground as described abovein Process B and acetic acid was optionally added as described inExamples 3-A to 3-D, below. The slurry or destabilized slurry was thenpressurized to 100 psig to 150 psig and fed into the confined reactionzone through the inlet (3) at a volumetric flow rate of 60 liter perhour (L/hr) such that the slurry or destabilized slurry was introducedas a high speed jet at 80 m/s into the reaction zone. At the same time,natural rubber latex concentrate (60CX12021 latex, 31 wt % dry rubbercontent, from Chemionics Corporation, Tallmadge, Ohio, diluted withdeionized water) was introduced into the second inlet (11) through aperistaltic pump at a volumetric flow rate of 106 L/hr and velocity of1.8 m/s. These rates were selected and flows were adjusted to yield anelastomer composite product comprising 50 phr (parts per hundred weightdry rubber) silica. The silica slurry or destabilized silica slurry andlatex were mixed by combining the low velocity latex flow and the highvelocity jet of silica slurry or destabilized slurry through entrainingthe latex flow in the jet of silica slurry or destabilized silica slurryat the point of impact. The production rate (on a dry material basis)was set at 50 kg/hr. Specific actual silica to rubber ratios in rubbercomposites produced by the process are listed in the Examples below. TGAwas performed following drying according to the Process B method.

Example 3-A

First Fluid: A destabilized aqueous dispersion of 25 wt % of silica with6.2 wt % (or 1.18 M) acetic acid was prepared as described in Process Bdescribed above. The zeta potential of the destabilized slurry was −14mV, indicating that the slurry was significantly destabilized by theacid. The destabilized silica slurry was pumped continuously underpressure into the first inlet (3).

Second Fluid: Elastomer latex was supplied to the reaction zone throughthe second inlet (11).

The first fluid impacted the second fluid in the reaction zone.

Results: A liquid to solid phase inversion occurred in the reaction zonewhen the destabilized silica slurry and latex were intimately mixed byentraining the low velocity latex flow into the high velocity jet ofdestabilized silica slurry. During the entrainment process, the silicawas intimately distributed into the latex and the mixture coagulatedinto a solid phase which contained 70 wt % to 85 wt % of water. As aresult, a flow of a solid silica-containing, continuous rubber phase ina worm or rope-like shape was obtained at the outlet of the reactionzone (13). The composite was elastic and could be stretched to 130% ofthe original length without breaking. TGA analysis on the dried productshowed the elastomer composite contained 58 phr of silica.

Example 3-B

First Fluid: A destabilized aqueous dispersion of 25 wt % of silica with6.2 wt % acetic acid was prepared according to Process B describedabove. The zeta potential of the slurry was −14 mV, indicating theslurry was significantly destabilized by the acid. The destabilizedsilica slurry was pumped continuously under pressure into the firstinlet (3).

Second Fluid: Elastomer latex was supplied to the reaction zone throughthe second inlet (11).

Third Fluid: Deionized water was also injected into the reaction zonethrough third inlet (14) at a volumetric flow rate of 60 L/hr and avelocity of 1.0 m/s.

The three fluids met and impacted each other in the reaction zone.

Results: A liquid to solid phase inversion occurred in the reaction zoneand a solid or semi-solid silica containing continuous rubber phase in arope or worm-like shape was obtained from the outlet of the reactionzone. A significant amount of cloudy liquid containing silica and/orlatex flowed out of the outlet (7) with the solid or semi-solidsilica-containing continuous rubber phase. The silica-containingcontinuous rubber phase contained about 70 wt % to about 75 wt % waterbased on the weight of the composite. TGA analysis on the dried productshowed the elastomer composite contained 44 phr of silica. Thus, theaddition of water through the third inlet had a negative impact on theprocess, yielding a product with lower silica content (44 phr incontrast to 58 phr in Example 3-A) and significant waste product.

Example 3-C

First Fluid: A 10 wt % acetic acid aqueous solution without silica wasprepared. A continuous feed of the acid fluid was pumped using aperistaltic pump at a volumetric flow rate of 60 L/hr through the thirdinlet (14) into the reaction zone at a velocity of 1.0 m/s at the timeof entry into the reaction zone.

Second Fluid: Elastomer latex was supplied to the reaction zone throughthe second inlet (11) by a peristaltic pump at a velocity of 1.8 m/s anda volumetric flow rate of 106 L/hr.

The two fluids met and impacted each other in the reaction zone.

Results: A solid worm-like, sticky rubber phase was formed. TGA analysison the dried product showed the solid rubber phase contained no silica.

Example 3-D

First Fluid: An aqueous dispersion of 25 wt % of silica without aceticacid was prepared according to Process B described above. The silicaslurry was pumped under pressure continuously into the first inlet (3)at a volumetric flow rate of 60 L/hr and at a velocity of 80 m/s at thepoint of entry into the reaction zone. The zeta potential of the slurrywas −32 mV, indicating that silica was stably dispersed in the slurry.Thus, in this Example 3-D, the silica slurry was not destabilized byaddition of acid to the slurry prior to impacting the latex fluid.

Second Fluid: Elastomer latex was supplied to the reaction zone throughthe second inlet (11) by a peristaltic pump at a velocity of 1.8 m/s anda volumetric flow rate of 106 L/hr.

Third fluid: After an initial period of continuous flow of the first andsecond fluids, a 10 wt % acetic acid aqueous solution was injectedthrough the third inlet (14) into the reaction zone at a volumetric flowrate that increased from 0 L/hr to 60 L/hr and a velocity that increasedfrom 0 m/s to 1.0 m/s. All three fluids impacted each other and mixed inthe reaction zone.

Results: Initially, prior to the injection of acid, no silica-containingcontinuous rubber phase formed and only cloudy liquid came out of thereaction zone outlet (7). Upon the injection of acid into the reactionzone (13), a worm-like, semi-solid silica-containing continuous rubberphase started to form as the flow of acetic acid through the third inletwas increased from 0 L/hr to 60 L/hr. The materials flowing from theoutlet still contained a significant amount of cloudy liquid, indicatinga significant amount of waste. TGA analysis of the dried product showedthat the silica-containing continuous rubber phase formed in thisexperimental run only contained 25 phr silica. Based on the productionconditions selected and the amount of silica used, if the silica hadbeen substantially incorporated into the silica-containing rubber phaseas in Example 3-A, the silica would have yielded a silica-containingrubber phase comprising in excess of 50 phr silica.

These experiments show that the silica slurry must be destabilized priorto initial impact with the elastomer latex in order to achieve thedesired silica-containing, continuous rubber phase. Example 3-A achievedwhat was considered efficient capture of the silica within the solidsilica-containing, continuous rubber phase, whereas Example 3-Dillustrates a comparative process utilizing an initially stable silicaslurry and demonstrating less than half of the efficiency of Example 3-Autilizing an initially destabilized silica slurry. The observation of acloudy liquid exiting the reaction zone exit point indicatesinsufficient mixing of the silica with the latex and a lower proportionof silica captured within the continuous rubber phase. It is theorizedthat in comparative processes 3B and 3D, there was insufficientdestabilization of fluids during mixing. The results further show thatpoor capture of silica occurs when additional fluid is added while thefirst fluid and second fluid are being mixed together, and such processconditions generate unwanted amounts of waste.

Example 4

In these examples, the process according to various embodiments of theinvention was run in the apparatus shown in either FIG. 1A or 1B undervarious conditions as described in Table 4, utilizing either Process Aor Process B described above. Operating conditions were selected toyield a solid or semi-solid silica-containing, continuous rubber phasewith the silica to rubber ratios set forth in Table 4.

TABLE 4 Silica^(a) Rubber Salt concentration Content in Latexconcentration Zeta in Latex wt % in Potential Process Slurry Latex (DRC)NH₃ Salt Slurry (Est.)^(b) Example A/B (wt %) Type (wt %) (wt %) Type(wt %) (mV) 4-1 A 20 Conc. 31.9 0.53 Ca(NO₃)₂ 1.0 −12.2 4-2 B 25 Conc.31 0.27 Ca(NO₃)₂ 0.75 −13.9 4-3 B 25 Field 33 0.60 N/A 0.00 −10.5 4-4 A18.5 Conc. 31 0.70 Ca(NO₃)₂ 0.75 −14.1 4-5 A 18.5 Conc. 30.6 0.70Ca(NO₃)₂ 0.39 −18.4 4-6 B 20 Conc. 31 0.27 Ca(NO₃)₂ 1 −1.8 4-7 A 20.0Conc. 31.9 0.53 Ca(NO₃)₂ 1 −12.2 4-8 A 10.0 Conc. 31.9 0.53 Ca(NO₃)₂ 0.5−17.1 4-9 A 10.0 Conc. 31.9 0.53 Ca(NO₃)₂ 0.5 −17.1 4-10 A 20.0 Field32.7 0.35 Ca(NO₃)₂ 1 −12.2 4-11 A 20.0 Field 32.7 0.35 Ca(NO₃)₂ 1 −12.24-12 A 20.0 Field 32.7 0.35 Ca(NO₃)₂ 1.3 −10.6 4-13 A 10.0 Field 32.70.35 Ca(NO₃)₂ 0.65 −15.4 4-14 A 10.0 Field 32.7 0.35 Ca(NO₃)₂ 0.65 −15.44-15 A 20.0 Conc. 31.9 0.53 N/A 0 −15.1 4-16 A 10.0 Conc. 31.9 0.53Ca(NO₃)₂ 0.55 −6.6 4-17 A 20.0 Field 32.7 0.33 N/A 0 −17.6 4-18 A 20.0Field 32.7 0.33 N/A 0 −17.6 4-19 A 20.0 Field 32.7 0.33 Ca(NO₃)₂ 1 −6.14-20 A 20.0 Field 32.7 0.33 Ca(NO₃)₂ 1 −6.1 4-21 A 20.0 Field 32.7 0.33Ca(NO₃)₂ 1 −6.1 4-22 A 16.0 Conc. 31.9 0.53 Ca(NO₃)₂ 1 −1.8 4-23 B 25Conc. 31 0.27 CaCl₂ 0.60 −12.8 4-24 B 25 Conc. 31 0.27 N/A 0 −10.6 4-25B 25 Conc. 31 0.27 N/A 0 −10.4 4-26 A 19.6 Field 32.8 0.66 Ca(NO₃)₂ 0.90−12.9 4-27 A 19.6 Field 32.8 0.66 Ca(NO₃)₂ 0.90 −12.9 4-28 B 25 Conc.30.5 0.27 Ca(NO₃)₂ 0.75 −13.9 4-29 B 25 Field 33.0 0.60 N/A 0.00 −9.84-30 B 25 Conc. 31.0 0.27 CaCl₂ 1.50 −6.9 4-31 B 25 Field 33.0 0.60 N/A0.00 −7.7 4-32 B 25 Conc. 31 0.27 N/A 0.00 −10.6 4-33 B 25 Conc. 31 0.27N/A 0.00 −10.4 4-34 B 25 Conc. 31.0 0.27 CaCl₂ 1.00 −9.5 4-35 A 18.5Conc. 30.6 0.70 Ca(NO₃)₂ 0.22 −22.0 4-36 B 25 Conc. 31 0.60 N/A 0.00−13.7 4-37 B 25 Conc. 31.0 0.27 Ca(NO₃)₂ 0.52 −12.8 4-38 A 15.0 Field32.8 0.66 N/A 0.00 −11.3 4-39 A 16.5 Conc. 30.6 0.68 N/A 0.00 −16.5 4-40B 25 Conc. 30.9 0.30 Al₂(SO₄)₃ 1.04 −5.0 4-41 B 15 Conc. 30.5 0.27 N/A0.00 −20.0 4-42 B 25 Conc. 30.5 0.27 Ca(NO₃)₂ 0.59 −3.0 4-43 B 25 Conc.31 0.27 Ca(NO₃)₂ 1.00 −12.1 Acid Slurry- wt % Inlet Actual Slurry Latexto-Latex in Acid/NH₃ Nozzle Silica Flow Flow Flow Acid Slurry molarVelocity^(c) loading Rate^(d) Rate^(d) Ratio Example Type (wt %) ratio(m/s) (phr) (L/hr) (L/hr) (v/v) 4-1 N/A 0 0.00 49 38.4 540 703 0.77 4-2N/A 0 0.00 75 86.3 60 59 1.01 4-3 Formic 2.5 1.45 11 69 60 76 0.79 4-4N/A 0 0 50 26 788 1541 0.51 4-5 N/A 0 0 47 45.6 827 1112 0.74 4-6 N/A 00.00 76 49.2 60 56 0.94 4-7 N/A 0 0.00 75 54.8 828 593 1.40 4-8 N/A 00.00 78 29.5 950 805 1.18 4-9 N/A 0 0.00 78 63.6 950 379 2.51 4-10 N/A 00.00 76 45.4 738 794 0.93 4-11 N/A 0 0.00 76 76.9 738 491 1.50 4-12 N/A0 0.00 76 38.2 738 938 0.79 4-13 N/A 0 0.00 78 52 950 484 1.96 4-14 N/A0 0.00 78 77.8 950 300 3.17 4-15 Acetic 4.70 4.01 75 25.4 828 593 1.404-16 Acetic 2.35 3.21 78 18.1 950 403 2.36 4-17 Acetic 2.80 3.14 75 54.8945 826 1.14 4-18 Acetic 2.80 3.93 75 67.2 945 660 1.43 4-19 Acetic 2.81.77 76 54.9 963 841 1.14 4-20 Acetic 2.8 2.36 76 43.3 630 734 0.86 4-21Acetic 2.8 1.77 76 34.0 630 978 0.64 4-22 N/A 0 0.00 117 46.6 966 7731.25 4-23 N/A 0 0.00 75 50.4 60 68 0.88 4-24 Formic 2.5 2.93 6475 605160 81 0.74 4-25 Formic 2.6 2.34 75 47 60 103 0.58 4-26 N/A 0 0.00 103110 1639 827 1.98 4-27 N/A 0 0.00 119 175 1902 648 2.94 4-28 N/A 0 0.0075 86.3 60 59 1.01 4-29 Formic 3.2 1.45 21 97 60 97 0.62 4-30 N/A 0 0 19138 60 43 1.38 4-31 Formic 7.1 1.45 29 27 60 214 0.28 4-32 Formic 2.54.19 75 ND 60 57 1.06 4-33 Formic 2.6 4.26 75 ND 60 57 1.06 4-34 N/A 00.00 19 122 60 37 1.63 4-35 N/A 0 0.00 87 ND 1090 932 1.17 4-36 acetic6.2 1.82 64 58 60 114 0.53 4-37 formic 0.9 1.47 29 ND 60 57 1.06 4-38formic 2.0 1.59 41 44 800 626 1.28 4-39 acetic 3.6 1.81 64 40.4 800 7431.08 4-40 N/A 0 0.00 29 ND 60 88 0.68 4-41 acetic 1.8 4.11 77 29 60 302.02 4-42 N/A 0 0 75 70.9 60 58 1.04 4-43 N/A 0 0 75 ND 60 142 0.42 N/A= not applicable ^(a)Examples 4-6 and 4-22 used Agilon 454 silica(precipitated silica treated with silane coupling agents, obtained fromPPG Industries Inc.). Examples 4-24 and 4-32 used Zeosil ® 175GR silica(conventional precipitated silica, obtained from Solvay S.A.). Examples4-25 and 4-33 used Zeosil ® Premium 200MP silica (HDS with high surfacearea of 200 m²/g, obtained from Solvay S.A.). Example 4-41 used Hi-Sil ®243LD silica (obtained from PPG Industries Inc, and Example 4-42 usedAgilon 400 silica (obtained from PPG Industries Inc). All other examplesused ZEOSIL ® Z1165 MP precipitated silica. Example 4-38 included 1.5 wt% (on a total slurry weight basis) N134 carbon black (Cabot Corporation)in the silica slurry. ^(b)Zeta potential values were estimated byinterpolation of experimentally determined curves of zeta potentialdependence on concentration of the salt or the acid of the slurries ofthe same grade of silica. ND = not determined, N/A = not applicable.^(c)The inlet nozzle velocity is the velocity of the silica slurry as itpasses through a nozzle (3a) at first inlet (3) to the reaction zone(13) prior to contacting the latex. ^(d)Slurry and Latex Flow Rates arethe volumetric flow rates in L/hour of the silica slurry and the latexfluid, respectively, as they are delivered to the reaction zone.

In all the examples except Examples 4-13 and 4-14, the selectedoperating conditions yielded a solid silica-containing, continuousrubber phase in a roughly cylindrical form. The product contained amajor amount of water, was elastic and compressible, and expelled waterand retained solids content when manually compressed. The solid materialcould be stretched, for example, the material of example 4-17 could bestretched or elongated to 130-150% of its original length, withoutbreaking. Silica particles were observed to be uniformly distributedthroughout a continuous rubber phase and this product was substantiallydevoid of free silica particles and larger silica grains, both onexterior and interior surfaces. In some of the examples (4-13 and 4-14),the selected operating conditions yielded a semi-solid product with apaste-like consistency, comprising a semi-solid silica-containing,continuous rubber phase. Silica particles were observed, on visualexamination, to be entrapped within, and uniformly distributedthroughout, the rubber phase. The semi-solid material expelled water andretained solids content upon further processing in one or moresubsequent operations selected to develop the paste-like material into asolid silica-containing continuous rubber phase. For the solid orsemi-solid silica-containing, continuous rubber phase to form, not onlydid the silica need to be destabilized (e.g., by prior treatment withacids and/or salts), but the volumetric flow rates of destabilizedsilica slurry relative to the latex had to be adjusted not only forachieving a desired silica to rubber ratio (phr) in the elastomercomposite, but also for balancing the degree of slurry destabilizationto the rate of slurry and latex mixing and the rate of coagulation oflatex rubber particles. By means of such adjustments, as the silicaslurry entrained the latex, intimately distributing silica particlesinto the rubber, the rubber in the latex became a solid or semi-solidcontinuous phase, all within a fraction of a second after combining thefluids in the confined volume of the reaction zone. Thus, the processformed unique silica elastomer composites by means of a continuous fluidimpact step done with sufficient velocity, selected fluid solidsconcentrations and volumes, and adjusted fluid flow rates to uniformlyand intimately distribute the fine particulate silica within the latexand, in parallel, as such distribution occurs, to cause a liquid tosolid phase inversion of the rubber.

Comparative Example 5

In these comparative examples, the same basic steps and apparatus asdescribed in Example 4 were used, but the combination of processconditions selected for each of the comparative examples in Table 5failed to create a solid or semi-solid continuous rubber phase, and asilica elastomer composite could not be produced. Table 5 below setsforth the concentration of silica in the slurry and the concentration ofacetic acid or calcium nitrate, if any, and other details of theseexamples.

TABLE 5 Rubber Acetic Silica content Salt Acid concentration of Latexconcentration concentration in Latex wt % in in Acid/NH₃ ComparativeProcess Slurry Latex (DRC) NH₃ Salt Slurry Slurry molar Example A/B (wt%) Type (wt %) (wt %) Type (wt %) (wt %) ratio 5-1 A 18.5 Conc. 30.60.70 Ca(NO₃)₂ 0.22 N/A 0 5-2 A 18.5 Conc. 30.6 0.70 Ca(NO₃)₂ 0.48 N/A 05-3 A 20.0 Field 32.7 0.35 Ca(NO₃)₂ 1 N/A 0 5-4 A 20.0 Field 32.7 0.35Ca(NO₃)₂ 1.3 N/A 0 5-5 A 10.0 Field 32.7 0.35 Ca(NO₃)₂ 0.65 N/A 0 5-6 A20.0 Conc. 31.9 0.53 N/A 0 4.70 0.66 5-7 A 20.0 Field 32.7 0.33 N/A 02.80 0.98 5-8 B 25 Conc. 31 0.27 N/A 0 0 0.00 5-9 A 18.5 Conc. 30.6 0.70N/A 0 0 0.00 5-10 A 18.5 Conc. 30.6 0.70 N/A 0 0 0.00 5-11 B 20 Conc.30.5 0.27 N/A 0 0 0.00 5-12 A 16.0 Conc. 31.9 0.53 N/A 0 0 0.00 ZetaInlet Slurry Slurry to Potential Nozzle Silica/Rubber Flow Latex FlowLatex Flow Comparative (Est.)^(a) velocity^(b) ratio setting Rate^(c)Rate^(c) Ratio Example (mV) (m/s) (phr) (L/hr) (L/hr) (v/v) 5-1 −22.0 6550 818 1118 0.73 5-2 −17.0 50 30 792 1807 0.44 5-3 −12.2 76 40 738 12890.57 5-4 −10.6 76 40 738 1289 0.57 5-5 −15.4 78 60 950 524 1.81 5-6−15.1 76 20 630 2255 0.28 5-7 −17.6 76 25 630 1761 0.36 5-8 −32.0 75 5060 114 0.53 5-9 −37 82 30 792 1807 0.44 5-10 −37 85 50 818 1118 0.735-11 −4.8 76 70 60 64 0.94 5-12 −7.9 67 50 552 619 0.89 N/A = notapplicable. ^(a)Zeta potential values were estimated by interpolation ofexperimentally determined curves of zeta potential dependence onconcentration of the salt or the acid of the slurries of the same gradeof silica. ^(b)The inlet nozzle velocity is the velocity of the silicaslurry as it passes through a nozzle (3a) at first inlet (3) to thereaction zone prior to contacting the latex. ^(c)Slurry and Latex FlowRates are the volumetric flow rates in L/hour of the silica slurry andthe latex fluid, respectively, as they are delivered to the reactionzone. ^(d)Examples 5-11 and 5-12 used Agilon ® 454 silica.

Comparative Examples 5-8, 5-9, and 5-10 show that withoutpre-destabilization of silica in the slurry, no silica-containingcontinuous rubber phase was produced, even when using the remainingprocess steps according to embodiments of the present invention.Comparative Examples 5-1, 5-2, 5-3, 5-4, 5-5, 5-6 and 5-7 show that evenwith prior destabilization of silica in the slurry (zeta potential ofsilica below 25 mV), a silica-containing continuous rubber phase couldnot be made with the combination of relative volumetric flow rates anddegree of dilution of the destabilization agent, (e.g., Ca(NO₃)₂ oracetic acid) in the reaction zone when fluids were mixed. Without beingbound to any theory, it is theorized that such a low concentration ofthe destabilization agent in the mixture of slurry and latex in thereaction zone may reduce the coagulation rate of latex rubber particlesso that a continuous rubber phase could not be formed within the shortresidence time in the reaction zone. In the Comparative Example 5-1,with 18.5 wt % of destabilized silica slurry and 30.6 wt % DRC latexconcentrate, a relative flow ratio of destabilized slurry to latex wasset at 0.73 (V/V) to deliver a silica to rubber ratio of 50 phr to thereaction zone. It is theorized that latex rubber particles did notcoagulate within the 0.48 second residence time of the mixture in thereaction zone at such relatively low volumetric flow ratio ofdestabilized slurry to latex, whereby the original concentration ofCa(NO₃)₂ of 14.8 mM in the destabilized silica slurry was diluted by 58%to 6.2 mM in the reaction zone. Thus, it was not possible under theseconditions to produce a solid or semi-solid silica-containing,continuous rubber phase comprising 50 phr silica. However, when a highersalt concentration (e.g., 0.5 wt % for Invention Example 4-8 versus 0.22wt % for Comparative Example 5-1) was used (zeta potential of −17.1 mVversus −22 mV), and the volumetric flow ratio of slurry to latex was setat 0.73 to produce 50 phr silica-containing rubber, suitable product wasmade. Comparative Example 5-3 shows that a solid silica-containing,continuous rubber phase could not be made at settings of 40 phr silicaand a volumetric flow ratio of destabilized slurry to field latex of0.57 (V/V), whereas such products were made when the flow ratio was 0.93and 1.50 thereby forming elastomer composite with 45.4 phr and 76.9 phrsilica, respectively, (Invention Examples 4-10 and 4-11). The higherslurry-to-latex volumetric flow ratios in the Inventive Examples 4-10and 4-11 led to less dilution of the salt in the reaction zone than inthe Comparative Example 5-3, thus producing a solid silica-containing,continuous rubber phase.

The salt concentration in the 18.5% destabilized silica slurry ofComparative Example 5-2 was 0.48%, with a zeta potential of −17 mV,indicating a degree of destabilization on par with those of InventionExamples 4-4 (−14.1 mV) and 4-5 (−18.4 mV), but no solidsilica-containing, continuous rubber phase was formed at a productionsetting of 30 phr silica content with latex concentrate at therelatively low flow ratio of selected for Comparative Example 5-2.Without wishing to be bound by any theory, it is believed that too muchdilution of the salt and/or destabilized silica slurry by latexconcentrate in the reaction zone in the Comparative Example 5-2 reducedthe coagulation rate of the rubber latex particles in the reaction zoneso much that a coherent continuous rubber phase would not form in theresidence time of 0.36 seconds within the reaction zone.

When mixing field latex with a 10 wt % silica slurry destabilized by0.65% Ca(NO₃)₂ (zeta potential at −15.4 mV), Comparative Example 5-5 didnot produce a solid silica-containing, continuous rubber phase at asilica to rubber ratio of 60 phr and slurry-to-latex volumetric flowratio of 0.57. These conditions did not deliver sufficient salt and/ordestabilized slurry to the reaction zone for rapid coagulation of therubber latex particles within the reaction zone. In general, either thedegree of silica slurry destabilization and/or slurry-to-latex flowratio adequate to coagulate latex concentrate were not sufficient tocoagulate field latex.

Similar results were obtained when acid was employed to destabilize thesilica slurry of Comparative Examples 5-6 and 5-7 and Invention Example4-17, respectively. When acid was used as the sole agent to destabilizethe silica slurry, there was a preferred threshold acid-to-ammonia molarratio in the mixture of the slurry and latex in the reaction zone, belowwhich solid or semi-solid silica-containing continuous rubber phasewould not form in the reaction zone. In these experiments, the thresholdacid-to-ammonia molar ratio that is desired was always higher than 1.0,with the result that the pH of the product exiting the reaction zone wasacidic. In the case of Comparative Examples 5-6 and 5-7, forsilica-to-rubber ratio production settings of 20 phr and 25 phr,relatively low slurry-to-latex volumetric flow ratios of 0.28 and 0.36were used, respectively. At these low flow ratios, the acidic slurry wasnot sufficiently acidic to neutralize the ammonia in the latex. Theacid-to-ammonia molar ratios for Comparative Examples 5-6 and 5-7 were0.66 and 0.98, respectively. In both cases, only cloudy liquid sprayedout of the reaction zone. In contrast, for the Invention Example 4-17, ahigher slurry-to-latex volumetric flow ratio of 1.14 was used forachieving 54.8 phr silica loading, through delivering sufficient acidfrom slurry into the reaction zone for neutralizing ammonia from latex.The acid-to-ammonia molar ratio in the reaction zone for the InventionExamples 4-17 was 3.14, and a solid silica-containing, continuous rubberphase was produced as an elastic worm-like material exiting the reactionzone. This material could be stretched to 130-150% of its originallength without breaking.

Example 6

To explore the process variables that enable formation of a solid orsemi-solid silica-containing continuous rubber phase, a series ofexperiments were conducted under various combinations of processvariables, including, but not limited to, concentration of silica in thedestabilized slurry, concentration of acid or salts in the destabilizedslurry, types of latex (e.g. field latex and latex concentrate),concentration of ammonia in latex, latex lots, flow rates ofdestabilized slurry and latex, velocities of destabilized slurry andlatex in reaction zone, and acid or salt concentrations in reactionzone. This series of experiments was carried out according to Process A,and calcium nitrate was used as the salt. The solid contents of fluidsand the inlet nozzle velocities for the experiments are listed in Tables6 and 7 for a latex concentrate and field latex, respectively. At a lowslurry to latex volumetric flow ratio (i.e., low silica to rubber ratioin the reaction zone), the destabilized slurry and salt were diluted bythe latex, and no solid or semi-solid silica-containing continuousrubber phase was formed. The setting for silica to rubber ratio was thengradually increased by raising the slurry-to-latex volumetric flow ratiountil a solid or semi-solid silica-containing, continuous rubber phasewas observed exiting the reaction zone. In Tables 6 and 7, the “SilicaLoading Delivered to Reaction Zone” indicates the lowestsilica-to-rubber ratio at which a solid or semi-solid silica-containing,continuous rubber phase was produced. The minimum salt concentration inthe reaction zone (including both destabilized slurry and latex) forformation of solid or semi-solid silica-containing, continuous rubberphase was calculated for each set of experimental conditions (e.g.,silica concentration in slurry, salt concentration in slurry, slurryvelocity). For the first six examples listed in Table 6, the silicaconcentration in the destabilized slurry was the same, namely 18.5 wt %,but the salt concentration in the destabilized slurry was varied, andthe silica loading lower threshold for formation of a solid orsemi-solid silica-containing, continuous rubber phase was determined ineach example by increasing the latex volumetric flow rate until coagulumwas formed. Results in Table 6 show that, when the salt concentration inthe destabilized silica slurry was increased from 0.22 wt % to 0.75 wt%, it was possible to reduce the slurry-to-latex volumetric flow ratio,so as to obtain a solid or semi-solid silica-containing, continuousrubber phase having a lower silica to rubber ratio. For instance, byincreasing the salt concentration from 0.22 wt % to 0.65 wt % of a 18.5wt % silica slurry, the minimum silica phr setting for creating a solidor semi-solid silica-containing continuous rubber phase decreased from80 phr silica to 35 phr silica as the relative volumetric flow of latexwas increased and the ratio of slurry-to-latex volumetric flow rates wasdecreased from 1.17 to 0.51. Similar results were observed for othersilica slurry concentrations and when acid was used to destabilize thesilica slurry.

Table 6. Solid or semi-solid silica-containing continuous rubber phaseformation thresholds: phr silica loading and calcium nitrateconcentration under various conditions when destabilized silica slurrywas mixed with 50% diluted latex concentrate (31 wt % dry rubbercontent; 0.70 wt % ammonia content except for last sample, for whichammonia content was 0.53 wt %) using Process A.

TABLE 6 Silica Silica Loading Slurry [Ca²⁺] Conc. [Ca²⁺] Zeta Deliveredto to latex Conc in In Ca(NO₃)₂ in Potential Inlet Nozzle Reaction flowReaction Slurry in Slurry slurry (Est.) Velocity Zone ratio Zone (wt %)(wt %) (mM) (mV) (m/s)^(a) (phr) (v/v) (mM) 18.5 0.22 14.8 −22.0 87 801.17 7.9 18.5 0.39 26.2 −18.4 46 46.3 0.68 10.5 18.5 0.48 32.3 −17.0 6740 0.59 11.9 18.5 0.52 34.9 −16.5 58 45 0.66 13.8 18.5 0.65 43.6 −15.158 35 0.51 14.7 18.5 0.75 50.4 −14.1 59 35 0.51 17.0 26 0.68 47.6 −14.554 55 0.55 16.8 26 0.99 69.3 −12.1 77 50 0.50 23.0 11 0.36 23.2 −19.1 8035 0.90 10.9 20 1.00 67.8 −12.2 49 35 0.49 22.2 ^(a)The inlet nozzlevelocity is the velocity of the silica slurry as it passes through anozzle (3a) at first inlet (3) to the reaction zone prior to contactingthe latex.

Table 7. Solid or semi-solid silica-containing continuous rubber phaseformation thresholds: phr silica loading and calcium nitrateconcentration under various conditions when silica slurry was mixed withfield latex using Process A.

TABLE 7 Silica Silica [Ca²⁺] Conc. [Ca²⁺] Zeta Inlet Loading Slurry Concin In Ca(NO₃)₂ in Potential Nozzle Lower to latex Reaction Slurry inSlurry slurry Slurry Velocity Threshold ratio Zone (wt %) (wt %) (mM)(mV) (m/s)^(a) (phr) (v/v) (mM) 10 0.65 41.7 −15.4 78 65 1.96 27.6 19.60.90 60.8 −12.9 71 65 0.95 29.6 20 1.0 67.7 −12.2 76 65 0.93 32.6 20 1.388.0 −10.6 76 50 0.72 36.7 ^(a)The inlet nozzle velocity is the velocityof the silica slurry as it passes through a nozzle (3a) at first inlet(3) to the reaction zone prior to contacting the latex.

In a batch mode coagulation experiment conducted by mixing silica slurrywith latex in a bucket under relatively low shear mixing, the minimumamount of the salt or acid to coagulate the latex in the mixture is aconstant, independent of original concentration of salt or acid in thesilica slurry before mixing. However, in processes according to variousembodiments of the invention, the threshold concentration of the salt inthe reaction zone for formation of a solid or semi-solidsilica-containing, continuous rubber phase increases with increases inthe salt concentration in the destabilized silica slurry before mixing(i.e. the degree of destabilization of silica slurry). For example, inTable 6, one can see that the threshold concentration of Ca(NO₃)₂ forcoagulating the latex concentrate is independent of silica concentrationin the destabilized slurry, but depends strongly on the original saltconcentration in the destabilized silica slurry. When the saltconcentration increased from 14.8 mM to 69.3 mM, the threshold saltconcentration increased from 7.9 mM to 23.0 mM. For comparison, a seriesof batch coagulation experiments were conducted in a bucket using lowshear stirring and it was determined that the threshold concentration ofCa(NO₃)₂ for coagulating the same latex concentrate was a constant at10.7 mM, independent of both the original salt concentration in thedestabilized silica slurry as well as the silica concentration in thedestabilized slurry. These results highlight the importance of balancingthe degree of destabilization of the silica slurry, rate of mixing, rateof silica particle agglomeration, and rate of latex coagulation underhigh shear for efficiently producing a solid or semi-solidsilica-containing, continuous rubber phase.

Likewise, the threshold acid-to-ammonia ratio for formation of a solidor semi-solid silica-containing, continuous rubber phase according toembodiments of the invention is not a constant, but increases with thedegree of acid destabilization of the silica slurry.

Based on the production variables described herein, such as the velocityof the destabilized silica slurry, the velocity of the latex, therelative flow rates of the destabilized silica slurry and latex fluids,the degree of destabilization of the silica slurry, the silicaconcentration in the destabilized slurry, the dry rubber content of thelatex, and the ammonia concentration of the latex (e.g., the ammoniaconcentration can be reduced by bubbling nitrogen through the latex oron top of the liquid surface), it was possible to obtain and/or predictformation of a solid or semi-solid silica-containing, continuous rubberphase over a range of desired silica loadings. Thus, the process of theinvention can be operated over an optimized range of variables.

Comparative Example 7

The following comparative experiments utilizing a multi-step batchprocess were conducted as a comparison to a continuous process accordingto embodiments of the invention.

In these comparative examples, a slurry of silica was combined withelastomer latex under batch mixing conditions, using either a silicaslurry that had been ground (as in the process of Process B above), or asilica slurry prepared without grinding, each at two slurryconcentrations: 25 wt % and 6 wt %, respectively (based on the totalweight of the slurry). The silica used in these examples was ZEOSIL®1165 MP. The elastomer latex used in all experiments was high ammonialatex concentrate (60CX12021, from Chemionics Corporation, Tallmadge,Ohio) diluted by 50% (by weight) with deionized water.

Experiment 7-A: Batch Mixing with Ground Silica Slurry

The silica slurry prepared above was mixed with a desired amount ofdeionized water in a 5 gallon bucket to achieve the target silicaconcentration of slurry.

For each run described below, the indicated quantity of silica slurrywas taken from the slurry run tank and mixed for fifteen minutes withthe indicated quantity of elastomer latex in a 5 gallon bucket—using anoverhead low shear stirrer (Model #1750, Arrow Engineering Co, Inc.,Hillside, N.J.). Except in Run 5, calcium chloride salt was then addedto the mixture and mixing continued until coagulation appeared to becomplete. Unless otherwise indicated, the salt was added as a 20 wt %salt solution in deionized water. The amount of salt used (dry amount)is indicated below. The “target phr silica” reflects the amount ofsilica in phr expected to be present in the rubber composite based onthe starting amount of silica used, assuming all silica was incorporatedinto all of the rubber. Runs 1-4 were dewatered and dried according tothe Process B methods described above.

Run 1—Target 55 phr silica rubber composite using 25 wt % silica slurry.

-   -   Conditions (for approx. 1.9 kg dried material):        -   2.7 kg of 25 wt % silica slurry, ground        -   4.0 kg of latex concentrate        -   0.060 kg (equivalent dry amount) of salt in solution.

Observations: Big pieces of wet rubber composite were formed around themixing blade after coagulation was complete. However, coagulation didnot incorporate all of the rubber and silica into the coagulum, as amilky liquid remained in the mixing bucket and a layer of wet silica wasdeposited on the bottom of the bucket. The dried coagulum weighed about0.5 kg, which was much less than the 1.9 kg targeted yield. Asignificant amount of silica appeared on the surface of the rubberproduct indicating poor distribution of silica within the rubbercomposite. The silica appeared to be very poorly mixed with rubber inthe coagulum, and undispersed grains of silica were felt and seenthroughout the coagulum. Silica particles were observed falling offdried coagulum. When dry rubber product was cut using a pair ofscissors, silica particles fell from the cut surface. Following drying,TGA analysis of the rubber product indicated loadings of silica averagedabout 44 phr.

Run 2—Target 70 phr silica rubber composite using 25 wt % silica slurry.

-   -   Conditions (for approx. 1.9 kg dried material):        -   3.1 kg of 25 wt % silica slurry, ground        -   3.6 kg of latex concentrate        -   0.060 kg of salt, added dry.

Observations: Big pieces of wet rubber were formed around the mixingblade and the post coagulation liquid was cloudy or milky. A layer ofsilica remained on the bottom of the bucket. Approximately 1 kg of driedcoagulum was produced. Similar to Run 1, very poor distribution ofsilica particles within the rubber coagulum was observed. Followingdrying, TGA analysis of the rubber product revealed silica loadingsaveraging about 53 phr.

Run 3—Target 55 phr silica rubber composite using 6 wt % silica slurry.

-   -   Conditions (for approx. 2 kg dried material):        -   2.6 kg of 25 wt % silica slurry, ground        -   8.4 kg deionized water        -   4.0 kg of latex concentrate        -   0.090 kg of salt in solution.

Observations: After adding the salt, the whole mixture of latex andslurry became a soft gel. About 0.9 kg dry composite was made. Similarto Run 1, very poor distribution of silica particles within the rubbercoagulum was observed. Following drying, the silica loading in thecoagulum measured by TGA was about 45 phr.

Run 4—Target 70 phr silica rubber composite using 6 wt % silica slurry.

-   -   Conditions (for approx. 2 kg dried material):        -   3.1 kg of 25 wt % silica slurry, ground        -   9.9 kg water        -   3.7 kg of latex concentrate        -   0.10 kg of salt in solution.

Observations: After adding the salt, small crumbs formed in milkyliquid. A sieve was used to collect and compact the small crumbs.Similar to Run 1, very poor dispersion of silica particles within therubber coagulum was observed. About 0.7 kg dry composite was collectedwith silica loading in the crumb measured by TGA at about 50 phr.

Run 5 Target 55 phr silica rubber composite using 25 wt % silica slurrydestabilized with 1% of CaCl₂.

-   -   Conditions (for approx. 1.9 kg dried material):    -   4.0 kg of 25 wt % slurry containing 1% CaCl₂, ground    -   2.7 kg latex concentrate.

Observations: The latex was put in a 5-gallon bucket with an overheadlow shear stir. The ground 25% destabilized silica slurry containing 1%of CaCl₂ was poured into the bucket with stirring, and stirringcontinued until coagulation was complete. Visual and tactileobservations of the rubber piece revealed many large pockets (mm to cmsize) of silica slurry within the rubber piece and a large quantity ofsilica particles trapped but not distributed within the solid rubberphase. The average silica loading in the dried coagulum measured by TGAwas about 58 phr. Sample-to-sample variations of silica loadings weregreater than 10 phr.

Experiment 7-B: Batch Mixing Using Silica Slurry without Grinding

For preparing the silica slurry without grinding, the silica was slowlyadded to water using only an overhead stirrer (Model #1750, ArrowEngineering Co, Inc., Hillside, N.J.). When the silica appeared to becompletely dispersed, the latex was added and the liquid mixture stirredfor 20 minutes. The CaCl₂ salt solution was then added to the liquidmixture and allowed to mix until coagulation appeared to be complete.Samples were dried in an oven prior to TGA analysis.

Run 5B—Target 65 phr silica rubber composition using 25 wt % silicaslurry.

-   -   Conditions (for approx. 1.9 kg dried material):        -   3.0 kg of 25 wt % silica slurry        -   3.8 kg of latex concentrate        -   0.06 kg of salt in solution.

Observations: After adding the salt, very large pieces of rubbercoagulum were formed around the blade of the stirrer. After coagulation,a thick layer of silica settled at the bottom of the bucket. The rubberpiece felt gritty and slimy. Grains of silica could be felt and seen onthe surface of the rubber coagulum and visual observation revealed verypoor distribution of silica in the rubber coagulum. The silica loadingin the coagulum was determined as 25 phr using TGA.

Run 6—Target 80 phr silica rubber composite using 25 wt % silica slurry.

-   -   Conditions (for approx. 1.9 kg dried material):        -   3.3 kg of 25 wt % silica slurry        -   3.4 kg of latex concentrate        -   0.06 kg of salt in solution.

Observations: The loading of silica in the rubber was determined as 35phr and visual observation revealed very poor distribution of silica inthe rubber coagulum.

Run 7—Target 110 phr silica rubber composite using 6 wt % silica slurry.

-   -   Conditions (for approx. 1.9 kg dried material, done in two        batches):        -   1.0 kg of 25 wt % silica slurry        -   15.6 kg of water        -   3.0 kg of latex concentrate        -   0.120 kg of salt in solution.

Observations: Small rubber crumbs were formed in the bucket and theliquid remaining after coagulation was mostly clear, with a layer ofsilica on the bottom of the bucket. TGA measured silica loading in therubber product averaged about 30 phr. The coagulum was elastic, withsilica grains on the surface. As it dried, silica could easily bebrushed off the surface, and visual observation revealed very poordistribution of silica in the rubber coagulum.

Run 8—Target 140 phr silica rubber composite using 6 wt % silica slurry.

-   -   Conditions (for approx. 1.9 kg dried material, done in two        batches):        -   1.0 kg of 25 wt % silica slurry        -   15.7 kg of water        -   2.4 kg of latex concentrate        -   0.110 kg of salt in solution.

Observations: Small rubber crumbs were formed in the bucket and theliquid remainder after coagulation was mostly clear, with a layer ofsilica on the bottom of the bucket. TGA measured silica loading in therubber product averaged about 35 phr. Particles of silica were settledon the surface of the rubber product that could be brushed free as itdried, and visual observation revealed very poor distribution of silicain the rubber coagulum.

Summary of Observations.

Compared with the continuous process of making elastomer composite, asfor instance in Examples 4 and 6, batch latex mixing process of Example7 were incapable of achieving the desired quality or quantity of silicadispersion in rubber. With ground silica slurries, the actual silicaloading in rubber products produced with batch mixing was observed to be<55 phr. After coagulation, a significant amount of silica settled atthe bottom of the mixing bucket and appeared on the surface of therubber product, indicating poor capture of silica particles within therubber coagulum. With silica slurries that had not been ground, theactual silica loading in rubber produced with batch mixing was limitedto 30 phr to 35 phr. After coagulation, a thick layer of silica settledat the bottom of the mixing bucket, the silica appeared to be verypoorly mixed with rubber in the coagulum, and undispersed grains ofsilica were felt and seen throughout the coagulum. Compared to processesaccording to embodiments of the present invention, batch mixingprocesses yielded poor incorporation and distribution of silicaparticles within the rubber matrix of the coagulum. In the product ofeach of these batch mixing runs, silica particles were observed fallingoff dried coagulum. When dry rubber composite was cut using a pair ofscissors, silica particles fell from the cut surface. Such loss ofsilica particles was not observed in examining the solid or semi-solidsilica-containing continuous rubber phase produced by processesaccording to embodiments of the invention.

Example 8

In these examples, the process to produce silica elastomer composite wasrun on the apparatus shown in either FIG. 1A or 1B under variousoperating conditions as described in Table 8, using either Process A orProcess B as described above. Operating conditions were selected toyield silica-containing continuous rubber phase with the silica torubber ratios set forth in Table 8. In each example, thesilica-containing continuous rubber phase comprised at least 40 wt %aqueous fluid. The approximate elongation at break of thesilica-containing continuous rubber phase emerging from the reactionzone is also given in Table 8.

TABLE 8 Silica^(a) Rubber Latex Salt Zeta concentration concentration wt% wt % in Potential Process in Slurry Latex in Latex NH₃ Slurry(Est.)^(b) Example A/B (wt %) Type (DRC) (wt %) (wt %) Salt Type (wt %)(mV) 8-1 B 25 Conc. 31 0.27 CaCl₂ 0.75 −11.4 8-2 B 25 Conc. 31 0.27CaCl₂ 0.75 −11.4 8-3 B 25 Conc. 31 0.27 CaCl₂ 1.0 −9.5 8-4 B 25 Conc. 310.27 N/A 0 −11.2 8-5 B 25 Conc. 31 0.27 N/A 0 −11.2 8-6 B 25 Conc. 310.27 N/A 0 −17.8 8-7 B 12.5 Conc. 31 0.27 CaCl₂ 0.50 8-8 A 20 Conc. 31.90.53 Ca(NO₃)₂ 1.0 −12.2 8-9 A 20.0 Field 32.7 0.33 N/A 0 −17.6 8-10 A20.0 Field 32.7 0.33 N/A 0 −17.6 8-11 A 20.0 Field 32.7 0.33 Ca(NO₃)₂ 1−6.1 8-12 A 20.0 Field 32.7 0.33 Ca(NO₃)₂ 1 −6.1 8-13 A 20.0 Field 32.70.33 Ca(NO₃)₂ 1 −6.1 8-14 B 25 Conc. 31.0 0.27 CaCl₂ 1.50 −6.9 8-15 B 25Conc. 31.0 0.27 CaCl₂ 1.00 −9.5 8-16 A 16.5 Conc. 30.6 0.68 N/A 0.00−16.5 8-17 B 25 Conc. 30.5 0.27 Ca(NO₃)₂ 0.59 −3.0 8-18 B 25 Conc. 310.27 Ca(NO₃)₂ 1.00 −12.1 Acid Slurry- Elongation wt % Inlet ActualSlurry Latex to-Latex @ Break in Acid/NH₃ Nozzle Silica Flow Flow Flowof Solid Acid Slurry molar Velocity^(c) loading Rate^(d) Rate^(d) RatioRubber Example Type (wt %) ratio (m/s) (phr) (L/hr) (L/hr) (v/v) Phase(%) 8-1 N/A 0 0.00 19 95 60 67 0.898 300-400 8-2 N/A 0 0.00 19 101 60 531.141 300-600 8-3 N/A 0 0.00 19 92 60 67 0.898 200-250 8-4 Formic 2.01.36 19 45 60 142 0.423 200-400 8-5 Formic 2.0 1.87 19 47 60 103 0.581150-250 8-6 Acetic 2.6 1.35 19 61 60 142 0.423 200-300 8-7 Acetic 1.31.86 37 33 60 48 1.245 300-400 8-8 N/A 0 0.00 49 38.4 540 703 0.77 1308-9 Acetic 2.80 3.14 75 54.8 945 826 1.14 130-150 8-10 Acetic 2.80 3.9375 67.2 945 660 1.43 120 8-11 Acetic 2.8 1.77 76 54.9 963 841 1.14 1208-12 Acetic 2.8 2.36 76 43.3 630 734 0.86 150 8-13 Acetic 2.8 1.77 7634.0 630 978 0.64 150-200 8-14 N/A 0 0 19 138 60 43 1.38 300-400 8-15N/A 0 0.00 19 122 60 37 1.63 300-500 8-16 acetic 3.6 1.81 64 40.4 800743 1.08 120-150 8-17 N/A 0 0 75 70.9 60 58 1.040 200-300 8-18 N/A 0 075 — 60 142 0.422 130-150 ^(a)Example 8-17 used Agilon 400 silica(obtained from PPG Industries Inc.). All other examples used ZEOSIL ®Z1165 MP precipitated silica. ^(b)Zeta potential values were estimatedby interpolation of experimentally determined curves of zeta potentialdependence on concentration of the salt or the acid of the slurries ofthe same grade of silica. ^(c)The inlet nozzle velocity is the velocityof the silica slurry as it passes through a nozzle (3a) at first inlet(3) to the reaction zone (13) prior to contacting the latex. ^(d)Slurryand Latex Flow Rates are the volumetric flow rates in L/hour of thesilica slurry and the latex fluid, respectively, as they are deliveredto the reaction zone.

The results show that highly elastic silica-containing continuous rubberphase materials in the form of solid articles can be achieved at avariety of operating conditions. Higher elongation is correlated withthe use of latex concentrate, lower production rates (rate of flow ofmaterial on a dry basis), increased residence time in the reaction zone,and/or lower flow rates of latex and/or destabilized silica slurry.

The present invention includes the followingaspects/embodiments/features in any order and/or in any combination, amethod of producing a silica elastomer composite, comprising:

-   (1) (a) providing a continuous flow under pressure of at least a    first fluid comprising a destabilized dispersion of silica in    particulate form, and having a wt % of silica of from about 6 wt %    to 35 wt % based on the weight of the first fluid, wherein said    silica has been obtained without drying said silica to a solids    content greater than 40%, by weight; and    -   (b) providing a continuous flow of at least a second fluid        comprising elastomer latex;    -   (c) providing volumetric flow of the first fluid relative to        that of the second fluid to yield a silica content of about 15        phr to about 180 phr in the silica elastomer composite;    -   (d) combining the first fluid flow and the second fluid flow        with a sufficiently energetic impact to distribute the silica        within the elastomer latex to obtain a flow of a solid        silica-containing continuous rubber phase or semi-solid        silica-containing continuous rubber phase.-   (2) The method, further comprising before step 1(a):    -   (a) acidifying a solution of silicate to obtain an aqueous        slurry of precipitated silica; and    -   (b) filtering said aqueous slurry of precipitated silica to        obtain precipitated silica in the form of a filter cake that has        a water content of from about 60 wt % to about 90 wt % based on        the weight of the filter cake.-   (3) The method, further comprising mechanically processing said    filter cake, whereby silica particle agglomeration, filter cake    viscosity, or a combination thereof, is reduced.-   (4) The method, further comprising adjusting acidity of the aqueous    slurry of precipitated silica.-   (5) The method, further comprising, before step 1(a):    -   (a) acidifying a solution of silicate to obtain an aqueous        slurry of precipitated silica having an initial ionic        concentration; and    -   (b) adjusting the initial ionic concentration of the aqueous        slurry of precipitated silica to yield a destabilized dispersion        of the precipitated silica having an ionic concentration of        about 10 mM to about 160 mM.-   (6) The method, further comprising before step 1(a):    -   (a) acidifying a solution of silicate to obtain an aqueous        slurry of precipitated silica;    -   (b) without drying the precipitated silica, adjusting the        aqueous slurry of precipitated silica to a solids content of        from about 6 wt % to about 35 wt %, to obtain a destabilized        dispersion of the precipitated silica.-   (7) The method, further comprising before step 1(a):    -   (a) acidifying a solution of silicate to obtain an aqueous        slurry of precipitated silica;    -   (b) recovering precipitated silica without forming a filter        cake.-   (8) The method, wherein said adjusting comprises filtering said    aqueous slurry of precipitated silica to obtain precipitated silica    in the form of a filter cake, washing the filter cake with an    aqueous medium and adjusting filter cake solids content and ionic    concentration to yield the first fluid.-   (9) The method, further comprising mechanically processing said    filter cake, whereby silica particle agglomeration, filter cake    viscosity, or a combination thereof, is reduced.-   (10) The method, further comprising before step 1(a):    -   (a) adding an aqueous silicate solution to an aqueous slurry of        carbon black particles to form a reaction mixture;    -   (b) adjusting the reaction mixture pH to deposit silica onto the        carbon black particles and yield an aqueous slurry of silica        coated carbon black particles having an initial ionic        concentration; and    -   (c) without drying the reaction mixture to a solids content of        greater than 40 wt %, adjusting the aqueous slurry of the silica        coated carbon black particles to a solids content of from about        6 wt % to about 35 wt %.-   (11) The method, wherein said silica is silica coated carbon black.-   (12) The method, further comprising adjusting the initial ionic    concentration of the aqueous slurry of precipitated silica to yield    a destabilized dispersion of silica coated carbon black particles    having an ionic concentration of about 10 mM to about 160 mM.-   (13) A method for making a rubber compound comprising    -   (a) conducting the method of claim 1, and    -   (b) blending the silica elastomer composite with other        components to form the rubber compound, wherein said other        components comprise at least one antioxidant.-   (14) The method, wherein at least one antioxidant has a lower    affinity to silica than 6PPD antioxidant.-   (15) The method, wherein said antioxidant comprises polymerized    2,2,4-trimethyl 1-1,2 dihydroquinoline or    2,6-di-t-butyl-4-methylphenol, 6PPD antioxidant, or a combination    thereof.-   (16) The method, wherein said silica is chemically treated with at    least one silane.-   (17) The method, wherein said silica is silane-treated prior to    carrying out step 1(a).-   (18) The method, said method further comprising subjecting    particulate silica to mechanical processing, whereby a controlled    silica particle size distribution is obtained prior to carrying out    step 1(a).

The present invention further includes a solid silica-containing rubberphase article made by the above methods and comprising at least 40 phrsilica dispersed in natural rubber and at least 40 wt % aqueous fluidand having a length dimension (L), wherein the solid silica-containingcontinuous rubber phase article can be stretched to at least 130% of (L)without breaking.

The present invention can include any combination of these variousfeatures or embodiments above and/or below as set forth in any sentencesand/or paragraphs herein. Any combination of disclosed features hereinis considered part of the present invention and no limitation isintended with respect to combinable features.

Applicants specifically incorporate the entire contents of all citedreferences in this disclosure. Further, when an amount, concentration,or other value or parameter is given as either a range, preferred range,or a list of upper preferable values and lower preferable values, thisis to be understood as specifically disclosing all ranges formed fromany pair of any upper range limit or preferred value and any lower rangelimit or preferred value, regardless of whether ranges are separatelydisclosed. Where a range of numerical values is recited herein, unlessotherwise stated, the range is intended to include the endpointsthereof, and all integers and fractions within the range. It is notintended that the scope of the invention be limited to the specificvalues recited when defining a range.

Other embodiments of the present invention will be apparent to thoseskilled in the art from consideration of the present specification andpractice of the present invention disclosed herein. It is intended thatthe present specification and examples be considered as exemplary onlywith a true scope and spirit of the invention being indicated by thefollowing claims and equivalents thereof.

1-77. (canceled)
 78. A method of producing a silica elastomer composite,comprising: providing a first fluid comprising a destabilized dispersionof silica with silica present in an amount of from 6 to 35 weightpercent, and said first fluid having a first fluid volumetric flow ratewherein said silica has been obtained without drying said silica to asolids content greater than 40%, by weight; and providing a second fluidcomprising an elastomer latex and said second fluid having a secondfluid volumetric flow rate, and combining under continuous flowconditions at least the first fluid and the second fluid to form asemi-solid silica-containing continuous rubber phase mixture, andforming said semi-solid silica-containing continuous rubber phasemixture into said silica elastomer composite in a mixing chamber of adevice, and recovering said silica elastomer composite having a silicacontent of from about 15 phr to about 180 phr.
 79. The method of claim78, wherein the destabilized dispersion is prepared by: (a) acidifying asolution of silicate to obtain an aqueous slurry of precipitated silica;and (b) filtering said aqueous slurry of precipitated silica to obtainprecipitated silica in the form of a filter cake that has a watercontent of from about 60 wt % to about 90 wt % based on the weight ofthe filter cake.
 80. A method for making a rubber compound comprising(a) conducting the method of claim 78, and (b) blending the silicaelastomer composite with other components to form the rubber compound,wherein said other components comprise at least one antioxidant.
 81. Themethod of claim 78, wherein said silica content of said silica elastomercomposite is from about 35 phr to about 115 phr.
 82. The method of claim78, wherein said silica content of said silica elastomer composite isfrom about 40 phr to about 115 phr.
 83. The method of claim 78, whereinsaid destabilized dispersion of silica comprises about 10 wt % to about28 wt % silica.
 84. The method of claim 78, wherein said first fluidcomprising said destabilized dispersion of silica has a zeta potentialmagnitude of less than 30 mV.
 85. The method of claim 78, wherein carbonblack is present in said silica elastomer composite in an amount of fromabout 10 wt % to about 0.1 wt % based on total particulates present insaid silica elastomer composite.
 86. The method of claim 78, whereinsaid elastomer latex is natural rubber latex.
 87. The method of claim86, wherein said natural rubber latex is in the form of a field latex,latex concentrate, desludged latex, chemically modified latex,enzymatically modified latex, or any combinations thereof.
 88. Themethod of claim 86, wherein said natural rubber latex is in the form ofan epoxidized natural rubber latex.
 89. The method of claim 86, whereinsaid natural rubber latex is in the form of a latex concentrate.
 90. Themethod of claim 78, further comprising mixing the silica elastomercomposite with additional elastomer to form an elastomer compositeblend.
 91. A method for making a rubber compound comprising (a)conducting the method of claim 78, and (b) blending the silica elastomercomposite with other components to form the rubber compound, whereinsaid other components comprise at least one antioxidant, sulfur, polymerother than an elastomer latex, catalyst, extender oil, resin, couplingagent, one or more additional elastomer composite(s), or reinforcingfiller, or any combinations thereof.
 92. A method for making a rubberarticle selected from tires, moldings, mounts, liners, conveyors, seals,or jackets, comprising (a) conducting the method of claim 78, and (b)compounding the silica elastomer composite with other components to forma compound, and (c) vulcanizing the compound to form said rubberarticle.
 93. The method of claim 78, further comprising conducting oneor more post processing steps after recovering the silica elastomercomposite.
 94. The method of claim 93, wherein the post processing stepscomprise at least one of: (a) dewatering the silica elastomer compositeto obtain a dewatered mixture; (b) mixing or compounding the dewateredmixture to obtain a compounded silica elastomer composite; (c) millingthe compounded silica elastomer composite to obtain a milled silicaelastomer composite; (d) granulating or mixing the milled silicaelastomer composite; (e) baling the silica elastomer composite after thegranulating or mixing to obtain a baled silica elastomer composite; (f)extruding the silica elastomer composite; (g) calendaring the silicaelastomer composite; and/or (h) optionally breaking apart the baledsilica elastomer composite and mixing with further components.
 95. Themethod of claim 93, wherein the post processing steps comprisecompressing the semi-solid silica-containing continuous rubber phase toremove from about 1 wt % to about 15 wt % of aqueous fluid containedtherein.
 96. The method of claim 78, further comprising the step ofconducting one or more of the following with the semi-solidsilica-containing continuous rubber phase: (a) transferring thesemi-solid silica-containing continuous rubber phase to a holding tankor container; (b) heating the semi-solid silica-containing continuousrubber phase to reduce water content; (c) subjecting the semi-solidsilica-containing continuous rubber phase to an acid bath; (d)mechanically working the semi-solid silica-containing continuous rubberphase to reduce water content.
 97. The method of claim 78, wherein saidsilica elastomer composite is a semi-solid silica-containing continuousrubber phase, and said method further comprising converting saidsemi-solid silica-containing continuous rubber phase to a solidsilica-containing continuous rubber phase.
 98. The method of claim 97,wherein said semi-solid silica-containing continuous rubber phase isconverted to said solid silica-containing continuous rubber phase bytreatment with an aqueous fluid comprising at least one acid, or atleast one salt, or a combination of at least one acid and at least onesalt.
 99. The method of claim 78, wherein said second fluid comprises ablend of two or more different elastomer lattices.
 100. The method ofclaim 78, wherein said process further comprises providing one or moreadditional fluids and combining the one or more additional fluids withsaid first fluid flow and second fluid flow, wherein said one or moreadditional fluids comprise one or more elastomer latex fluids, and saidadditional fluids are the same as or different from said elastomer latexpresent in said second fluid flow.